Resected solitary pulmonary nodules which histologically are granulomas and in which acid-fast bacilli are seen are usually assumed to be due to infection with Mycobacterium tuberculosis. We reviewed the culture results of all resected lung specimens submitted to the mycobacteriology laboratory from 1969 to 1979. Of the 20 specimens in which acid-fast bacilli were seen and which roentgenographically were solitary pulmonary nodules, 12 (60 percent) were due to infection with M. avium-intracellulare. In five granulomas, acid-fast bacilli were seen but failed to grow on culture. In one instance each, M. tuberculosis, M. fortuitum and M. gordonae grow on culture. Fiberoptic bronchoscopy was not diagnostic in 10 patients, although in one patient M. avium-intracellulare was cultured from the bronchial washings. Lymph nodes removed at mediastinoscopy from 12 patients did not contain granulomas. Since the physician was often unaware that cultures subsequently grew nontuberculous mycobacteria, most patients were treated with two drug regimens for presumed tuberculosis. Postoperative follow-up was available for 14 of the 20 patients, for a period ranging from four months to 10 years. There was no instance of dissemination of the infection to lung or pleura. We conclude that solitary pulmonary "tuberculomas" are often due to nontuberculous mycobacterial infection, particularly M. avium-intracellulare. When the lesion is due to nontuberculous mycobacteria and can be resected in its entirety, drug therapy is not indicated.