Proctitis frequently appears in inflammatory bowel diseases, mainly in ulcerative colitis. On the other hand, an increased incidence of sexually transmitted infections (STIs) has been described, which can start as proctitis. Additionally, the infectious etiology includes fecal-oral transmission pathogens as proctitis triggers. Similarly, non-infectious causes also play a role in the etiopathogenesis. The case is described of a 34-year-old man whit HIV on antiretroviral treatment, raising questions regarding management and the need to clarify the diagnosis in the context of a condition that was inadequately advancing and ultimately culminated in an unexpected turn of events, revealing that the cause of his ailment was one of the most common sexually transmitted infections (STIs) worldwide, with accessible diagnosis and treatment. The patient was treated with antimicrobials for 3 weeks and showed favorable improvement.