The following are the events in professional sumo during the year 2008.
- Hatsu basho, Ryogoku Kokugikan, Tokyo, 13 January – 27 January
- Haru basho, Osaka Prefectural Gymnasium, Osaka, 9 March – 23 March
- Natsu basho, Ryogoku Kokugikan, Tokyo, 11 May – 25 May
- Nagoya basho, Aichi Prefectural Gymnasium, Nagoya, 13 July – 27 July
- Aki basho, Ryogoku Kokugikan, Tokyo, 14 September – 28 September
- Kyushu basho, Fukuoka International Centre, Kyushu, 9 November – 23 November
Hakuho on the opening day of the January tournament
- 27th: Yokozuna Asashoryu, making his return from a two tournament suspension, enters the final day of the Hatsu basho in Tokyo in the joint lead for the championship, but is defeated by fellow yokozuna Hakuho, who wins his sixth top division yusho with a 14–1 record. Asashoryu finishes on 13–2 with runner-up honours. Another Mongolian, Kakuryu, wins 11 matches and receives the Technique Award. Rank-and-filer Takekaze scores 12–3 and wins the Fighting Spirit Award, and Kisenosato scores 10–5 and receives the Outstanding Performance Award for his victory over Asashoryu on the 2nd day. Georgian Tochinoshin, making his debut in the second highest juryo division, wins the yusho with a 12–3 record. Yamamotoyama takes the makushita division championship with a perfect 7–0 record. Announcing their retirements from active competition are former top division wrestlers Tochinohana, Tochisakae, Kobo and Chiyotenzan, as well as Kyokutenho's brother Fudoyama and Tamanoshima's brother Tamamitsukuni.
- 2nd: The danpatsu-shiki or retirement ceremony of former ozeki Tochiazuma takes place at a packed Kokugikan.
- 7th: The former head of the Tokitsukaze stable, Junichi Yamamoto, and three non sekitori wrestlers from the stable are arrested on charges of assault leading to the death of trainee Tokitaizan. The Aichi Prefecture Police Department allege that on 25 June 2007, the night before his death, Tokitaizan was struck on the head with a beer bottle and then tied to a pole and beaten with a wooden stick, on the orders of Yamamoto. The following day Tokitaizan was forced into an intense 30 minute training session and repeatedly hit in the face, kicked and beaten with an aluminium bat, resulting in his collapse and death.
- 10th: Asashoryu wins a one-day tournament held at the Ryogoku Kokugikan, defeating Miyabiyama, Asasekiryu and Tokitenku.
Baruto was a runner-up in March
- 23rd: In a reversal of fortunes from the January tournament in Tokyo, Asashoryu defeats Hakuho on the final day in Osaka to win his 22nd yusho, and his first since July 2007, with a 13–2 score. Hakuho finishes runner-up on 12–3, level with the maegashira Kokkai and Baruto, who each receive a share of the Fighting Spirit Award. Tochiozan wins 11 bouts and the Technique Award, while sekiwake Kotoshogiku is awarded the Outstanding Performance prize for being the first wrestler to beat Asashoryu on Day 12. Ozeki Kotoōshū withdraws through injury with only two wins, meaning he will be kadoban (in danger of demotion) in May. Kimurayama wins his first juryo division championship. Announcing their retirements are former maegashira Shunketsu, and makushita wrestler Asahimaru, an extremely successful amateur champion who missed the whole of 2003 through injury and was never able to make the sekitori ranks.
- 26: Bulgarian Kotooshu bounces back from his disappointing performance in March to win his first top division championship with a 14–1 record, becoming the first European to do so. His only defeat was to Aminishiki on Day 13, who wins his third Outstanding Performance Award. Asashoryu and Hakuho finish behind the pace on 11–4 and attract controversy after bad-temperedly pushing and glaring at each other after their match on the final day. Toyonoshima also wins 11 bouts and receives the Fighting Spirit Award. Kisenosato is also awarded the Fighting Spirit prize for his 10–5 mark at the rank of komusubi, while sekiwake Ama earns his third Technique Award. In the juryo division Chiyohakuho wins his first yusho, and former maegashira Tamaasuka wins the makushita championship.
- 27: The head of the Sumo Association sees both Asashoryu and Hakuho separately and gives each a strict warning over their conduct in the previous day's bout.
- 2nd: Asashoryu uses his position as head of the wrestlers union to call for all salaried rikishi to be given a pay raise of ten percent (which would be their first pay raise since 2001) to compensate for the rising cost of food and fuel. The Sumo Association are reportedly unimpressed with his remarks.
- 27th: Hakuho wins the tournament held in Nagoya with a perfect 15–0 record. His yokozuna rival Asashoryu withdraws after a defeat to Tochinonada on day 5, citing an injury to his elbow. Talk of Kotooshu's possible promotion to yokozuna is silenced after he turns in a mediocre 9–6 score. Ozeki Kotomitsuki finishes as runner-up to Hakuho, but four wins behind. Ama wins another Technique award and scores 10–5, while Toyonoshima also finishes on 10–5 and receives the Outstanding Performance prize. The Fighting Spirit award goes to maegashira Toyohibiki for his ten wins. Veteran Bushuyama wins the juryo division championship. Former maegashira Satoyama wins the makushita yusho, defeating Yamamotoyama, amongst others, in a playoff. Yamamotoyama is nonetheless promoted to the juryo division after the tournament.
- 18th: Russian maegashira Wakanoho is arrested for cannabis possession after his wallet, lost in June, is turned in to police and found to contain a cigarette mixed with the illegal drug. Police search his home and discover more evidence of cannabis use.
- 21st: The elders of the Sumo Association meet and decide on the immediate dismissal of Wakanoho. His name is removed from the banzuke ranking sheets for the September tournament, with the Maegashira 8 East position left blank. His stablemaster Magaki (the former yokozuna Wakanohana II) steps down from the Association's board of directors.
- 28th: Asashoryu defeats Hakuho in a playoff to win an exhibition tournament held in Mongolia and receives a trophy from Mongolian President Nambaryn Enkhbayar. The tournament attracts live television and front-page newspaper coverage in Mongolia.
- 2nd: Drug tests are carried out on all sekitori ranked wrestlers in the wake of Wakanoho's dismissal, and two other Russian wrestlers, brothers Roho and Hakurozan, test positive for cannabis.
- 8th: The Sumo Association announce the immediate dismissals of Roho and Hakurozan, who both deny ever taking banned substances. The head of the Sumo Association Kitanoumi, who is also Hakurozan's stablemaster, announces his resignation, although he remains on the board of directors. He is replaced as chairman by Musashigawa (former yokozuna Mienoumi). On the same day, police charges against Wakanoho are dropped due to his age and the small quantity of the drug found in his possession, and he is released from jail.
- 10th: Wakanoho visits the Sumo Association and asks to be readmitted to sumo, but his request is turned down.
- 11th: Wakanoho files a lawsuit against the Sumo Association claiming unfair dismissal.
- 14th: The Aki basho opens, without Wakanoho, Roho or Hakurozan. New chairman Musashigawa announces that judges have been instructed to call back any wrestlers who do not perform the tachi-ai properly and make them start the bout again. This leads to a large number of false starts and criticism from commentators over the new rules.
- 28th: Hakuho wins the tournament with a 14–1 record. Once again he does not have to face Asashoryu, who withdraws on Day 10, prompting speculation about his possible retirement. Ama finishes as runner-up with twelve wins and wins the Outstanding Performance Award, and is seen as a candidate for promotion to ozeki next time. Goeido takes the Fighting Spirit prize. The one remaining Russian sekitori, Aran, wins the juryo championship. Veteran former sekiwake Tamakasuga announces his retirement.
- 28th: The small Araiso stable closes, as its stablemaster is approaching the mandatory retirement age.
- 29th: At a press conference, the former Wakanoho alleges he was involved in match-fixing or yaocho, which he details in a series of interviews with the tabloid Shukan Gendai. The opponents he names all deny the allegations.
- 30th: Three external directors are added to the Sumo Association's board, as demanded by the Ministry of Education after the recent scandals.
- 3rd: In the first ever court appearance by a yokozuna, Asashoryu takes the stand on behalf of the Sumo Association in a lawsuit brought against the Shukan Gendai over separate match-fixing allegations made by the magazine in January 2007. He denies ever taking part in rigged bouts, calling the allegations "complete lies." (In March 2009 a judge rules in favour of the Sumo Association.)
- 6th: Asashoryu travels to his homeland of Mongolia to receive treatment for his injured elbow. He sits out this month's regional tour and also misses the Kyushu honbasho.
- 7th: The trial begins in the Nagoya District Court of the three wrestlers from the Tokitsukaze stable alleged to have caused bodily injury resulting in the death of trainee Tokitaizan, real name Takashi Saito. The three admit wrongdoing but say they were only following the orders of their former stablemaster Junichi Yamamoto, who denies the charges and is being tried at a later date.
- 28th: Roho and Hakurozan launch a lawsuit against the Sumo Association seeking their re-admission to sumo.
- 29th: The Tokyo District Court turns down Wakanoho's lawsuit seeking to nullify his dismissal by the Sumo Association.
- 23rd: In the Kyushu basho in Fukuoka Hakuho wins his third straight championship, defeating Ama in a playoff after both men finish with 13–2 records. Ama seals his promotion to ozeki and receives the Technique Prize. Asashoryu misses the tournament, and ozeki Kaio pulls out after three days. Aminishiki wins the Outstanding Performance Award, and maegashira Yoshikaze gets the Fighting Spirit Prize for his fine 11–4 score. Mongolian Shotenro wins the juryo yusho at his first attempt.
- 26th: Ama's promotion to ozeki is officially confirmed. To mark the occasion his ring name is changed to Harumafuji.
- 28th: Wakanoho retracts all his match-fixing allegations and issues an apology.
- 10th: The Tokyo High Court rejects an appeal brought by Wakanoho over a lower court ruling that his dismissal from sumo was fair.
- 18th: The three Tokitsukaze stable wrestlers are found guilty and given suspended sentences of between two and a half and three years. All are also dismissed from the Sumo Association.
- 19th: The Sumo Association announces the cancellation of the scheduled overseas exhibition tournament in London that was due to take place in 2009, because of uncertainties caused by the financial crisis. it is the first time a foreign jungyo has been cancelled.