OBJECTIVE Non-Hodgkin's lymphoma is a common complication in patients with HIV infection. The purpose of this study was to analyze the abdominal CT findings in a large series of patients with this condition. METHODS We retrospectively reviewed the abdominal CT examinations of 110 men and two women (21-62 years old; average, 39 years) with untreated AIDS-related lymphoma, as defined by the Centers for Disease Control. Lymphoma was the initial AIDS-defining illness in 79% of the patients. RESULTS Abdominal CT scans showed normal findings or only mild enlargement of the liver or spleen in 36% of the 112 patients, whereas evidence of intraabdominal lymphoma was seen in 64%. Evidence of focal lymphomatous involvement was seen on abdominal CT scans in 58 (98%) of 59 patients in whom the predominant signs and symptoms were related to the abdomen and in 14 (26%) of 53 patients with extraabdominal signs or symptoms. In the 64% of patients with evidence of intraabdominal lymphoma, lymph node enlargement was seen in 56% and extranodal disease was seen in 86%. Extranodal sites of involvement in the 72 patients with evidence of intraabdominal lymphoma included the gastrointestinal tract (54%), liver (29%), kidney (11%), adrenal gland (11%), lower genitourinary tract (10%), spleen (7%), peritoneum and omentum (7%), pancreas (5%), epidural space (4%), bone (3%), and muscle (1%). Mild enlargement of the liver or spleen was present in a minority of cases. Moderate or marked hepatomegaly (cephalocaudal span > 20 cm) and splenomegaly (cephalocaudal span > 15 cm) were even less common and occurred only in the presence of focal hepatic lesions. CONCLUSIONS Our results show that AIDS-related lymphoma may affect any abdominal organ, most commonly lymph nodes, the gastrointestinal tract, liver, kidney, and adrenal gland. Hepatic or splenic enlargement was uncommon and was not often seen as an isolated finding in the absence of evidence of abdominal lymphoma.