Multiple inflammatory skin lesions and osteomyelitis of the right ankle developed in a 51-year-old man who had been receiving prednisone therapy for several months. Cultures of both the skin and bone lesions yielded Mycobacterium szulgai, a scotochromogenic mycobacterium, which is an unusual human pathogen. The patient's condition responded to treatment with isoniazid, ethambutol hydrochloride, and rifampin.