During a 12 year period from January 1962 to December 1973, 48 patients with atypical mycobacterial infection of the lung were treated surgically with excellent results. There were no deaths, and sputum conversion was achieved in all of them. The considerable drug resistance of the atypical mycobacteria and the possible ill effects of prolonged conservative treatment in cases with active disease and drug resistant organisms are pointed out. Early surgical treatment is recommended in such circumstances. Some bacterioligical and biological characteristics of atypical mycobacteria are also discussed.