To investigate the usefulness of bronchoscopy for the diagnosis of Mycobacterium avium complex (MAC) pulmonary disease, we retrospectively reviewed the clinical charts, and radiographic and bacteriologic findings of all patients who were admitted to our hospital between 1994 and 2000, and who fulfilled the 1997 American Thoracic Society (ATS) criteria for MAC pulmonary infection. A total of 132 patients were diagnosed as affected by MAC pulmonary disease during that period. Of these, bronchoscopic examination was performed in those patients who showed negative sputum smear for mycobacteria on three consecutive days (n = 43) or who could not expectorate sputum (n = 2). Of 42 patients, sputum culture was positive for MAC in 34 patients (81.0%). Bronchial washing sample was smear-positive for MAC in 17 of 39 patients (43.6%), and culture-positive for MAC in 33 of the 39 patients (84.6%). Transbronchial lung biopsy (TBLB) specimens revealed specific findings (epithelioid cell granuloma and/or acid-fast bacilli) in 14 of 38 patients (36.9%). Bronchial washing of all patients who showed specific histology in TBLB grew MAC in culture. Based on the bronchoscopic examination, we could diagnose MAC pulmonary disease in 36 patients. In addition, smear and polymerase chain reaction (PCR) results of bronchial washing made possible an early diagnosis of MAC pulmonary disease in 15 patients. We examined the relation of CT findings to bronchial washing results. Isolation of MAC in bronchial washing is significantly related to small nodular opacity around the ectatic bronchi on the CT scan (p = 0.016). In our retrospective study, in sputum smear-negative patients with MAC pulmonary disease, MAC isolation by culture of bronchial washing was no more frequent than that with sputum culture. However, bronchial washing is useful to differentiate infection from casual isolation of MAC. In addition, we could make early diagnosis of MAC pulmonary disease based on smear and PCR results of bronchial washing. To make a diagnosis of MAC, bronchial washing is superior to TBLB, and should be done in the bronchus which drains the area revealing small nodular opacity around ectatic bronchi.