Diabetic patients may develop a painful mass in the leg as a manifestation of spontaneous infarction of muscle. Experience with six patients with focal infarction of muscle without peripheral gangrene has demonstrated a stereotyped clinical presentation. The use of an open muscle biopsy to confirm the diagnosis has been associated with increased signs and symptoms. Clinical exacerbations occur during vigorous physical therapy. We delineate the characteristic clinical and pathologic findings and the course of the illness with emphasis on the importance of recognition of the syndrome so that biopsy and overzealous therapy are avoided.