Klippel-Trenaunay syndrome is a congenital vascular anomaly characterized by a triad of varicose veins, cutaneous capillary malformation, and hypertrophy of bone and soft tissue. Gastrointestinal and genitourinary vascular malformations in Klippel-Trenaunay syndrome may present with lower gastrointestinal bleeding and hematuria. The majority of patients with splenic hemangiomatosis are asymptomatic. We herein report a case admitted to the Gastroenterology Clinic with life-threatening hematochezia and symptomatic iron deficiency anemia. The patient's history was remarkable for subtotal cystectomy and enterocystoplasty in December 2002 for vascular malformation, located in the bladder, which presented with hematuria. Although the patient was also diagnosed with colonic varices and splenic hemangiomas at that time, due to the asymptomatic mild intermittent hematochezia and splenic hemangiomas, the patient did not seek any help for rectal bleeding until her admittance to our department for evaluation of massive lower gastrointestinal bleeding. Endoscopy revealed vascular malformations starting from the transitional zone in the rectum extending up to the descending colon. Due to this extensive involvement of the rectum and sigmoid colon, no interventional endoscopic procedure was attempted and she was referred to surgery. A very low anterior resection. with double stapling technique was done. Postoperative follow-up has been uneventful for six months since the operation. To the best of our knowledge, this is the first Klippel-Trenaunay syndrome case presenting with lower gastrointestinal bleeding, hematuria and splenic hemangiomas. The literature on the evaluation and management of lower gastrointestinal and genitourinary bleeding in Klippel-Trenaunay syndrome is reviewed.