Adenovirus colitis in the acquired immunodeficiency syndrome. Adenovirus was identified in colonic tissue by transmission electron microscopy or culture in 5 of 67 (7.4%) homosexual men seropositive for human immunodeficiency virus (51 with the acquired immunodeficiency syndrome) with diarrhea. Colonoscopy showed the mucosa to be normal in 3 cases and mildly inflamed in 2. Light microscopy showed foci of mucosal necrosis that contained chronic inflammatory cells and degenerating and necrotic epithelial cells with amphophilic nuclear inclusions. By transmission electron microscopy, hexagonal viral particles characteristic of adenovirus were identified within the inclusions. Only 1 patient was concomitantly infected by a second potential enteric pathogen. It was concluded that adenovirus, an uncommon enteric pathogen in immunocompetent adults, causes intestinal pathology and may be associated with diarrheal illness in persons with the acquired immunodeficiency syndrome. 