A 40-year-old heterosexual man, with a personal history of human immunodeficiency virus (HIV) infection under antiretroviral therapy (stage A2 of the CDC (Centers for Disease Control and Prevention) classification), presented with complaints of tenesmus and rectal bleeding. The patient underwent a colonoscopy that identified an ulcerated lesion of the distal rectum, beginning above the pectinate line, friable, with raised and irregular edges, about 4 cm in length, occupying half the circumference of the lumen (see Fig. 1). The biopsies performed revealed only chronic idiopathic ulceration, without typical characteristics of solitary rectal ulcer. In the histological material, no microorganisms or neoplastic cells were identified and the Warthin-Starry stain and the immunohistochemistry investigation of cytomegalovirus or herpes virus infection were negative, as well as polymerase chain reaction (PCR) and culture for mycobacteria. The microbiological study of feces was negative, as were viral serologies. Pelvic magnetic resonance imaging identified a slight thickening of the distal rectum, with no other changes. No specific therapy was performed and symptoms progressively improved. The ulcer was reassessed by sigmoidoscopy at 6 and 9 months, with spontaneous partial healing (see Fig. 2). The biopsies were repeated, with overlapping results, as well as negative microbiological study. During this time, the patient maintained antiretroviral therapy and stable CD4 counts. The diagnosis of idiopathic rectal ulcer in an HIV patient was assumed. After 24 months of follow-up, the patient remains asymptomatic, without recurrence of rectal ulceration.