Despite the success of lung transplantation, infection is one of the leading causes of morbidity and mortality. Mycobacterial infections have been reported rarely, with the majority due to Mycobacterium tuberculosis. Our aim was to assess the incidence, etiology, and clinical outcome of mycobacterial infection after lung transplantation; to do so, we have studied retrospectively all lung and heart- lung transplants performed over a 12-yr period between November 1986 and June 1998 (n = 261). Twenty-three patients (9%) (M:F, 11:12) were diagnosed with mycobacterial infections in 25 sites, including n = 19, pulmonary (M. avium complex [n = 13], M. tuberculosis [n = 2], M. abscessus [n = 2], M. asiaticum [n = 1], and M. kansasii [n = 1]) and n = 6 extrapulmonary (M. haemophilum [n = 5] and M. abscessus [n = 1]) infections. Time to diagnosis from transplantation was 677 +/- 735 d (range, 2- 3,086 d). Three episodes of transient colonization with M. avium were not treated; the remaining (22 of 25, 88%) were treated. Initial baseline therapy for nontuberculous mycobacteria included clarithromycin, rifampicin, ciprofloxacin, and/or ethambutol. All cutaneous lesions resolved completely, while clinical and graft function improved in 11 of 16 (69%) and 8 of 16 (50%) of patients treated, respectively. Seventeen of 23 patients (72%) survived at a follow-up of 1,658 +/- 759 d (range, 522-3,285 d). Complications, predominantly due to rifampicin, included gastrointestinal intolerance and an increased tendency for rejection. There were no deaths attributable to mycobacterial disease or therapy. We conclude that mycobacterial infection, particularly due to nontuberculous mycobacteria, is relatively common after lung transplantation and may be an unrecognized cause of graft dysfunction. Early treatment of cutaneous lesions is associated with excellent control; however, graft dysfunction may be permanent. Although drug toxicity and interactions with immunosuppressive agents were not infrequent, the majority of these infections can be managed successfully.