From June 1994 to June 2002, disseminated infections due to non-tuberculous mycobacteria (NTM) were diagnosed in 42 of 716 (5.9%) non-haemophiliac HIV-infected patients aged > or =15 years who were treated at National Taiwan University Hospital. The median age of these patients was 35 years (range, 27 to 60 years). The median CD4+ cell count and plasma viral load at the time of diagnosis of disseminated NTM infections were 8 x 10(6)/L (range, 0 to 892 x 10(6)/L) and 37,600 copies/mL (range, <400 to >750,000 copies/mL), respectively. The nadir CD4+ count during the observation period was 6 x 10(6)/L (range, 0 to 30 x 10(6)/L). The species of NTM isolated included Mycobacterium avium complex (MAC) [n = 35], Mycobacterium kansasii (4), Mycobacterium chelonae (1), Mycobacterium abscessus (1), and unidentified NTM (3). Co-infection with 2 species of NTM was diagnosed in 2 patients. NTMs were isolated from blood (n = 18), liver (18), lymph node (12), bone marrow (10), cerebral spinal fluid (1), ascites (1), and pericardial effusion (1). The median duration of antimycobacterial therapy of the 42 patients was 7 months (range, 0 to 24 months). Mortality during the study period was greater in the patients enrolled before highly active antiretroviral therapy (HAART) was introduced (14 of 15, 93%) than in those who received HAART (9 of 27, 33%). As of December 31, 2002, 15 patients (35.7%) had discontinued secondary prophylaxis against disseminated NTM infections when their median CD4+ count had increased to 119 x 10(6)/L (range, 25 to 465 x 10(6)/L), and 86.7% (13/15) of the patients had achieved an undetectable plasma viral load after HAART. During the median observation duration of 12 months (range, 2 to 57 months), none of the 15 patients had relapse of disseminated NTM infections. Our findings indicate that disseminated NTM infections without primary prophylaxis were associated with a high mortality rate, especially before HAART became available. In patients who received HAART and had a favorable response with viral suppression and immune restoration, discontinuation of secondary prophylaxis against disseminated NTM infections was safe.