A case of Klippel–Trenaunay syndrome in a 20-year-old girl was described in this article. The clinical data showed that she had suffered from circuitous and dilated veins in her right leg since birth. The radiologic investigations demonstrated multiple circuitous and dilated blood vessels above the condylus medialis femoris, and associated with secondary bone changes. It was regarded as Klippel–Trenaunay syndrome according to clinical history and imaging findings. Klippel–Trenaunay syndrome is a rare congenital peripheral vascular disease, and the relevant literature is reviewed. Klippel–Trenaunay syndrome needs to be distinguished from other vascular diseases.