This study aimed to confirm the isolation of nontuberculous mycobacteria (NTM) from patients with pneumoconiosis. Monthly sputum examinations in 155 patients were performed from April 1998 to December 2002. When NTM were isolated, species were identified and the frequency of isolation was reviewed. We then identified the patients who satisfied the bacteriologic criteria for the diagnosis of nontuberculous mycobacterial pulmonary disease (NTM pulmonary disease) recommended by the American Thoracic Society (ATS). Symptoms and findings on computed tomography (CT) scans were evaluated. NTM were isolated from 60 patients (39%): common etiologic species defined by the ATS, i.e., Mycobacterium avium, M. intracellulare, M. abscessus, and M. kansasii, were identified in 21 patients; unusual etiologic species, i.e., M. fortuitum, M. simiae, and M. szulgai, were identified in 11 patients; and undefined species, which appeared to be nonpathogenic, were identified in 41 patients. The bacteriologic criteria were satisfied in 8 patients. NTM species isolated in conformity with the bacteriologic criteria were: M. avium in 4 patients, M. intracellulare in 2, a combination of M. intracellulare and M. kansasii in 1, and M. gordonae in 1 patient. Two patients, from whom M. avium were repeatedly isolated, satisfied the ATS diagnostic criteria for NTM pulmonary disease. It is important to note that NTM, including both pathogenic species and nonpathogenic species, were isolated from patients with pneumoconiosis.