A case of multiple osteomyelitides due to Mycobacterium avium (M. avium) infection with osteosclerotic bone lesions is reported. A 67-year-old male had been suffering from persistent fever and back pain since October 1999, and 20.0-2.5 mg prednisolone per day was prescribed for continuous inflammatory symptoms in January 2000. Six months later, computed tomography revealed osteosclerotic lesions in the left femur and thoracic vertebrae, but no skin lesion associated with mastocytosis or internal malignancy was identified. In September of 2002, a dome-shaped, soft subcutaneous tumor developed on the upper sternum. Histopathological findings revealed subcutaneous adipose tissue with several foci of tiny abscesses. Two weeks later, creamy pus was discharged through a draining sinus at the center of the wound. M. avium was demonstrated in the pus by Zeel-Nielsen staining and microplate hybridization.