Leiomyosarcoma is a rare, poorly studied malignancy derived from smooth muscle cells, prone to recurrence and metastasis. Of superficial neoplasms, soft tissue leiomyosarcomas account for no more than 2.3%, while tumors of vascular origin, which mainly occur in large veins, account for 0.5% to 0.7% of cases. In the practice of a vascular surgeon or phlebologist, patients often have a combined pathology of the lower extremities (chronic venous disease, atherosclerotic obliterans of the lower extremity arteries, varicose disease, gonarthrosis, etc.). The article presents a clinical case of soft tissue leiomyosarcoma of the inguinal region in a patient treated for the left lower extremity varicose vein disease shortly before the detection of a tumor. The possibility that any physician may encounter a patient in need of treatment for a rare malignancy such as soft tissue leiomyosarcoma has been shown.