The experience with pulmonary disease caused by Mycobacterium avium complex (MAC-PD) was examined over a 12-yr period in a nonreferral setting. The 29 patients with the disease constituted 30% of all pleuropulmonary mycobacterioses. The mean annual incidence rate was 1/100,000. Sixty-two percent of patients were female, the majority of whom had no discernible preexisting pulmonary disorder to account for their susceptibility. A short- and long-term favorable response to therapy was observed in more than 90% of the 16 patients treated with intent to cure. Suggested as plausible explanations for the favorable response rate compared with previous studies originating in referral settings were: absence of adverse selection as shown by a smaller proportion of patients with far-advanced cavitary disease or with previous treatment failure, and a larger proportion of female patients. A previously unreported pattern of MAC-PD was observed: disease limited to the lingula or middle lobe occurred in 21% of the patients, all female. A rarely identified pattern, primary disease in a 3-yr-old exposed to pet birds, is reported.