The present paper deals with observations on six patients with infiltrating angiolipomata. The lesion represents a distinct clinicopathological entity characterized by the replacement of skeletal muscle and infiltration of tissue planes by mature fat combined with variable angiomatous and collagenous components. These tumors occur chiefly in the first three decades of life and involve predominantly the lower extremities. Because of swelling, pain, impairment of function, and focal areas of calcification or ossification, they may be confused preoperatively with malignant tumors. The lesions, although benign, tend to recur unless completely excised. They differ clinically and histologically from the pure primary anigiomata of skeletal muscle.