Klippel-Trenaunay syndrome is a congenital vascular anomaly characterized by a triad of varicose veins, cutaneous capillary malformation, and hypertrophy of bone and (or) soft tissue. Gastrointestinal vascular malformations in Klippel-Trenaunay syndrome may present with gastrointestinal bleeding. The majority of patients with spleenic hemangiomatosis and/or left inferior vena cava are asymptomatic. We herein report a case admitted to the gastroenterology clinic with life-threatening hematochezia and symptomatic iron deficiency anemia. Due to the asymptomatic mild intermittent hematochezia, splenic hemangiomas and left inferior vena cava, the patient did not seek any help for gastrointestinal bleeding until his admittance to our department for evaluation of massive gastrointestinal bleeding. He was referred to angiography because of his serious pathogenetic condition and inefficiency of medical therapy. The method showed that hemostasis was successfully achieved in the hemorrhage site by embolism of corresponding vessels. Further endoscopy revealed vascular malformations starting from the stomach to the descending colon. On the other hand, computed tomography revealed splenic hemangiomas and left inferior vena cava. To the best of our knowledge, this is the first Klippel-Trenaunay syndrome case presenting with gastrointestinal bleeding, splenic hemangiomas and left inferior vena cava. The literature on the evaluation and management of this case is reviewed.