We studied the clinical characteristics of nine patients with pulmonary Mycobacterium avium complex disease occurring in association with corticosteroid drugs collected from our associated hospitals during the past 6 years. The average age of the nine patients was 62.2 years and the male/female ratio was 3 : 6. Regarding underlying disease, respiratory diseases existed in four of the patients and nonrespiratory diseases in the other five patients. The duration of corticosteroid treatment ranged from 5 months to 5 years, and the total dose of corticosteroid drugs ranged from 1.78 to 43.20 g. Pulmonary Mycobacterium avium complex disease was detected by clinical symptoms during corticosteroid treatment in six patients, and purified protein derivative was positive in three of eight patients tested. Radiological findings showed an infiltration shadow without cavity and bronchiectasis in the lower lung field. Microbiological examination was smear-positive in three patients, and the isolated mycobacterium was Mycobacterium intracellulare in five patients and Mycobacterium avium in four. Tolerance was shown to all antituberculous drugs, except for clarithromycin, in all patients. Although treatment including clarithromycin was performed for seven patients, the sputum conversion rate was 33% and an improved clinical effect was noted in only one patient. No change occurred in four and worsening occurred in four. Attention should be paid to the clinical symptoms and radiological findings of patients who have received corticosteroid drugs over a long period of time, because pulmonary Mycobacterium avium complex is characterized by atypical radiographic findings with no relationship to the total dose or duration of the administered corticosteroid drugs.