The incidence of diseases caused by nontuberculous mycobacteria (NTM) is increasing worldwide. There has been no previous report regarding the clinical significance and disease spectrum of these bacteria in Taiwan. From January 1992 to June 1996, 201 isolates of NTM were recovered from clinical specimens from 143 patients at National Taiwan University Hospital. We retrospectively studied the clinical records and radiographs of these patients. A total of 86 isolates of NTM were considered clinically significant; they were cultured from 39 patients with soft-tissue infections and/or osteomyelitis (16 patients), isolated pulmonary infections (10), keratitis (6), disseminated infections (4), peritonitis, enteritis, and conjunctivitis. The most common organisms involved in these patients were Mycobacterium fortuitum complex, followed by Mycobacterium avium-intracellulare. Positive cultures of NTM were derived from respiratory sources (sputum, bronchial washing, and pleural effusion) from 111 patients; in 11 the isolates were associated with clinically significant disease, in two they were persistent colonizers, in 79 the isolates were considered to be contaminants, and for the remainder there were insufficient cultures to classify. The organisms involved in pulmonary diseases were M. avium-intracellular (4 patients), Mycobacterium chelonae (1), Mycobacterium abscessus (1), M. fortuitum (2), Mycobacterium gordonae (1), and unidentified scotochromogens (2), M. fortuitum complex (55%) was the most common pathogen of keratitis and soft-tissue infection. Three of the four cases of disseminated disease were caused by M. avium-intracellulare. The only isolate of Mycobacterium kansasii found in this study was a contaminant. The strains of clinically significant NTM isolates found in our hospital and their disease spectrum differ from those reported in other regions of the world.