Our aim was to evaluate the efficacy of abdominal US and fine-needle aspiration biopsy (FNAB) in the diagnosis of disseminated mycobacteriosis (DM) in patients with Acquired Immunodeficiency Syndrome (AIDS). We reviewed the US and clinical records of 18 AIDS patients (12 males; 22-43 years) with DM studied with abdominal US. 18 patients underwent fine-needle aspiration biopsy of enlarged abdominal lymphnodes and 11 underwent FNAB of the spleen. All aspirates were studied with acid-fast stain for fast examination and cultures for isolation of mycobacteria. Abdominal US showed: enlarged abdominal lymphnodes (diameter range: 5-35 mm; mean 17 mm) splenomegaly (spleen diameter range: 14-22 cm; mean: 16.2 cm) and hepatomegaly (right hepatic lobe thickness range: 14.5-18.5 cm) in all patients; multiple splenic abscesses (diameter range: 3-20 mm) in 11 patients; small intestine wall thickening in 5 patients (maximum bowel wall thickness range: 7-15 mm); mild to moderate ascites in 8 patients; pleural effusion in 4 patients; hyperechogenicity of the kidney cortex in 5 patients; peritoneal abscesses in one and a retroperitoneal abscess in one patient. fast-acid-stain of spleen and/or lymphnode FNAB specimens allowed early diagnosis of mycobateriosis in 18/18 cases (100%). Cultures of lymphnode aspirates grew mycobacteria in 10/18 patients (56%). Spleen aspirates grew mycobacteria in 11/11 patients (100%) Blood cultures were positive in 6/18 patients (33%). Diagnosis of species was M. tuberculosis in 9 and M. avium in 6 patients. In 3/18 patients (17%) all cultures were negative. In conclusion, abdominal US features suggest DM in AIDS patients. Spleen and/or lymphnode FNAB allows a specific diagnosis in 100% of the patients.