We analyzed clinical and microbiological features of six cases involving Mycobacterium fortuitum isolated from sputum or surgical lung specimen. Patients were five men and one woman with an average age of 59. Four cases had a history of pulmonary tuberculosis and three had nontuberculous mycobacterial lung disease. Three out of six cases had underlying chronic obstructive pulmonary disease. Diabetes mellitus was complicated in five cases. All diseases were in the upper lobes of either lung. Clinical symptoms were mainly cough and sputum, while two cases developed pneumothorax. Although all strains showed low sensitivity to standard anti-tuberculous agents, chemotherapy including those drugs or fluoroquinolones and macrolides were successful in all treated cases.