BACKGROUND: Ulcerative colitis (UC) is one of the major types of inflammatory bowel diseases and is associated with a significantly increased risk of not only lymphoproliferative disorders but also lymphomas, of which most cases are related to the long-term usage of immunosuppressants. Here, we demonstrate a very rare case of other iatrogenic immunodeficiency-associated colonic diffuse large B-cell lymphoma (Oii-DLBCL) complicating UC and rectal perforation. In addition, we reviewed the clinicopathological features of previous cases of DLBCL related to UC. CASE PRESENTATION: A 68-year-old man was diagnosed with left-sided UC 26 months prior. Although he was followed by immunosuppressive therapy with azathioprine and infliximab, an emergency total proctocolectomy was performed due to rectal perforation. The resected specimen exhibited irregular wall thickening and elevated multinodular lesions extending from the mid-transverse colon to the rectum, measuring up to 52 cm in length. Histologically, the lesion was diagnosed as Oii-DLBCL and crypt abscess surrounded by mixed inflammatory cell was remained. CONCLUSION: Oii-DLBCL complicating UC with rectal perforation is extremely rare. Macro- and microscopic findings are important for early diagnosis of the lesion.