During the 15 year period from January, 1976 to September, 1990, we treated 77 patients with atypical mycobacteriosis (AM) of the lung surgically with satisfactory results. There were 56 men and 20 women, a ratio of 2.9 : 1. The age of the patients ranged from 20 to 76, with an average of 50.7 years. The operative rate was 3.7% against the patients admitted with a diagnosis of atypical mycobacterial infection. The number of the patients and the types of bacilli classified according to Runyon's criteria were 4 for Group I (M. kansasii), 63 for Group III (M. avium complex), 3 for Group IV, and 7 unknown. The operative indications we adopted were, 1) the resistance to most antituberculotics, 2) localized lesion, and 3) progressive deteriorations. Sensitivity study showed that over 90% of the patients had bacilli with complete or incomplete resistance against all antituberculotics except cycloserine. The area of major involvement was localized in the upper lobe in 47, but was bilateral in 14 patients. The period of conservative therapy prior to the surgical treatment ranged from 2 to 164 months, with an average of 28 months. As to the operative procedures, 58 had lobectomy, 12 pneumonectomy , 11 segmentectomy or wedge resection, 12 thoracoplasty, and 17 combined procedures. The incidence of post-operative complication was 16.9%. The recurrences were observed in 8 patients (10.4%), who had multiple and bilateral lesions. Complete cure rate was 83.1% and 64 patients were able to resume normal life. Our results indicate that, if properly selected, time required for the treatment may become shorter and the patients with AM may get better results by surgical treatment.