Mycobacterial infections are common in people with impaired cell-mediated immunity. Bone marrow transplant recipients have this defect and might be expected to have a high incidence of mycobacterial infections. We reviewed mycobacterial infections in 2241 BMT recipients at the University of Minnesota Hospital. Mycobacterial infections were diagnosed in 11 (0.49%), including nine of 1486 allograft recipients (0.6%) and two of 755 (0.26%) autograft recipients. Two patients had M. tuberculosis infection, two, M. avium-intracellulare infection and seven, infection with rapid growing atypical mycobacteria (M. fortuitum or M. chelonae). The manifestations included unexplained fever, pulmonary infiltrates, osteomyelitis or central venous catheter tunnel inflammation. Six of the seven infections with rapid growing atypical mycobacteria were related to central venous catheters. Appropriate local measures and therapy with antimycobacterial medications resulted in complete resolution of infection in the nine patients treated. The low incidence of mycobacterial infection observed in BMT recipients contrasts with that observed in people with impaired cell-mediated immunity.