Aneurysmal dilatation of a localized segment of a vein occurring in the absence of associated varicose vein is a rare phenomenon. A case of venous aneurysm of the left long saphenous vein is presented. A 47-year-old male was admitted to our hospital, with the cheif complaint of swelling in the left femoral triangle. In the erect position a fluctuating mass appeared along the proximal portion of the left long saphenous vein, when the patient coughs, a trembling imparted to the palpating fingers was observed. Venography demonstrated a saccular dilatation of the long saphenous vein arising 4cm below connection with the femoral vein. A 3cm portion of the long saphenous vein containing the aneurysm was removed. Histologically, the internal wall of the aneurysm was lined with intimal cell layer and it was confirmed to be true venous aneurysm.