Diffuse cavernous hemangioma of the rectum (DCHR) is a relatively rare disease. A 40-year-old man presented with long-standing lower abdominal discomfort and hematuria. At the time of hospitalization, his vital signs and hemoglobin level were normal. Colonoscopy showed markedly dilated blood vessels in the sigmoid mucosa, which was confirmed on magnetic resonance imaging and computed tomography as cavernous hemangioma. Without surgery, there have been no signs of progression of DCHR during a 3-year follow-up period.