Klippel-Trenaunay syndrome (KTS) is a rare, vascular malformation. The major clinical presentation is an overgrowth involving the extremities. The diagnosis of KTS was based on an imaging study, which revealed vascular malformations. The author’s report is of a 36-year Thai man with; hypertrophy of the right lower extremity, whilst having suffered from two-months of bloody defecation. The magnetic resonance imaging showed venous malformations with soft tissue hypertrophy of the affected limb, genitalia and rectum. The patient was diagnosed with: KTS accompanied by gastrointestinal complications.