From 1969 to 1978, 24 patients were suspected of having pulmonary disease caused by atypical mycobacteria. Seven were infected with Mycobacterium avium-intracellulare, six with Mycobacterium avium, six with Mycobacterium scrofulaceum, two with Mycobacterium fortuitum, and one with Mycobacterium gordonae. One patient had a strain of scotochromogens antigenically related to Mycobacterium simiae. Mycobacterium kansasii was found in only one patient. Retrospective analysis revealed that 20 of the patients had preexisting pulmonary diseases, including 16 who had tuberculosis. Disease caused by atypical mycobacteria is rare in Thailand, and possible reasons for the rarity are discussed.