Enteric infection with adherent bacteria has been seen in a person with chronic diarrhea who was infected with the human immunodeficiency virus. In this study, adherent bacteria were seen in 17% of all patients with AIDS evaluated during a 1-year period. The infection was centered in the cecum and right colon. Three distinct histopathologic patterns of adherence were observed: attaching and effacing lesions, bacteria intercalated between microvilli, and aggregates of bacteria more loosely attached to the damaged epithelium. The infections were associated with weight loss (P < .005) and peripheral blood CD4+ cell of counts < 100/mm3 (P < .05). Eight of 9 patients treated with antibiotics had symptomatic improvement. Bacterial cultures of rectal biopsies frozen at endoscopy yielded Escherichia coli in 12 of 18 cases; aggregative adherence was seen in 6. Isolates from 2 cases hybridized with a DNA probe encoding aggregative properties. These results suggest that chronic infection with adherent bacteria may produce a syndrome of AIDS-associated diarrhea and wasting.