Klippel-Trenaunay syndrome (KTS) is a rare congenital disease, that is characterized by capillary malformations as “port wine stain”, vascular anomalies mostly as varicose vein and bone and soft tissue hypertrophy of one lower extremity. A 23-year-old female complained of leg edema and extensive varicose veins of left leg. She has had the “port wine stain” of left leg from birth. Despite her leg length is not different, she was diagnosed to have Klippel-Trenaunay syndrome. Ultrasounds findings presented enlarged “lateral marginal vein (LMV)”, that has severe regurgitation and incompetence perforator through the hip muscle connecting to the proximal site of LMV. Ultrasound showed slight enlargement of soleal vein, but deep vein was intact. She underwent endovenous laser ablation for the enlarged LMV. Her leg edema and varicose vein improved without any complication. Endovenous laser ablation is a safe and effective therapy for KTS patients who had anomalous vein such as LMV. Evaluation of deep vein is very important to decide the intervention. Because if deep vein has any problem, ablation of anomalous vein could lead to complications. Ultrasound scan imaging can examine the venous conduits with the patient in standing position and is possible in even small clinics. In this case, the patient was not followed-up in childhood despite she has “port wine stain”. We recommend that KTS patients should receive care by a multidisciplinary team including vascular specialists and pediatricians from childhood.