Of the 36 patients with human immunodeficiency virus (HIV) infection admitted to our institution since 1985, one had a non-spinal psoas abscess due to Mycobacterium tuberculosis without pulmonary involvement. A 32-year-old male homosexual had prolonged fever and weight loss for two months. Serologic tests for antibodies against HIV were positive. A characteristic hypodense lesion within the right psoas muscle was noted by computerized tomographic (CT) scanning. Diagnosis of psoas abscess was confirmed by ultrasound-guided needle aspiration. The smear of the aspirated pus showed numerous acid-fast bacilli and cultures grew M. tuberculosis. The lesion responded rapidly to antituberculous therapy and a follow-up CT scan 10 months later showed improvement.