Gastrointestinal histoplasmosis (GIH) is common in patients with disseminated disease but only rarely comes to clinical attention due to the lack of specific signs and symptoms. We report the unusual case of a 33-year-old Caucasian male with advanced AIDS who presented with upper GI bleeding from diffuse erosions throughout the duodenum. Biopsy of the lesions revealed small bowel mucosa with granulomatous inflammation and macrophages with small intracellular yeasts consistent with disseminated histoplasmosis. The patient demonstrated significant clinical improvement following a two-week course of liposomal amphotericin B. To our knowledge, this is the first case report of duodenal histoplasmosis leading to clinically significant bleeding, manifesting with worsening anemia and melanotic stools. Given our findings, we maintain that GIH should be considered on the differential diagnosis for GI bleeding in AIDS patients at risk, specifically those with advanced immunosuppression (i.e., CD4(+) cell counts <100 cells/mm(3)) who reside in endemic areas (Ohio or Mississippi river valleys) and/or have a prior history of histoplasmosis. For diagnostic evaluation, we recommend checking a urine Histoplasma quantitative antigen EIA as well as upper and/or lower endoscopy with biopsy. We recommend treatment with a two-week course of liposomal amphotericin B followed by indefinite itraconazole.