Peripheral vascular leiomyosarcomas are rare. Two cases of intramural leiomyosarcomas of the great saphenous vein are described. The first case is considered a high-grade sarcoma, based on the high mitotic index on histologic study. The second case presents only infrequent mitoses on light microscopy. Immunohistochemical analysis for factor VIII helped to establish the diagnosis. Characteristics of the tumor and differential diagnosis are discussed. Treatment consisted of wide local excision. Radiotherapy and chemotherapy were given to the patient with high-grade tumor.