In the evaluation of patients with a painful atraumatic mass in an extremity, the clinician should consider a number of clinical entities: primary tumor of muscle, focal or localized nodular myositis, local muscular abscess or soft-tissue infection, osteomyelitis, and thrombophlebitis. A rare complication of diabetes, viz, diabetic muscular infarction, heretofore not reported in the rheumatic disease literature is reviewed. This entity is compared with the conditions of focal and localized nodular myositis, which are nearly as rare.