Purpose: To report the incidence, clinical importance and management of the incompetent gastrocnemius vein.Methods: The incompetency was examined by duplex and pulse-Doppler ultrasound at the popliteal fossa in a standing position between July 2006 and August 2014.Results: Among 1805 legs surveyed, 14 legs showed primary incompetent gastrocnemius vein (0.78%). The incompetency was in medial gastrocnemius vein in 13 legs (93%). Clinical manifestation was varicose vein in the small saphenous territory in nine, varicose vein in great saphenous territory in one, congestive dermatitis in two, calf clamp in one and no symptom in one. The nine cases with varicose vein in the small saphenous territory received surgical management. These included three cases with residual varicose veins after saphenopopliteal disconnection and stripping small saphenous vein. The root of the gastrocnemius vein was divided leaving no complication. In cases without varicose vein in small saphenous territory, an elastic compression socks was useful in some degree.Conclusions: Incompetency of gastrocnemius vein was not so rare. When a case is accompanied by small saphenous varicose veins, division of the root of gastrocnemius vein along with small saphenous vein stripping is recommended in order to reduce residual varicose vein.