This report describes the case of a 21-year-old man with a history of Sturge-Weber syndrome and varicose veins. Examination of the left lower limb revealed the presence of significant port-wine staining, and hypertrophy. Duplex examination revealed a severely hypoplastic deep venous system with a tortuous, dilated, long saphenous vein, which was competent and responsible for a significant proportion of venous return from the left lower limb, thus confirming the diagnosis of Klippel-Trenaunay syndrome. The patient was counseled regarding the implications of the diagnosis and was treated conservatively. The association between these two rare syndromes has been previously reported in the nonvascular literature. We believe that features of the Sturge-Weber syndrome or other forms of mesodermal phakomatosis should alert a clinician to the presence of lower limb venous malformations, which will need to be investigated prior to embarking on what could be potentially detrimental venous surgery.