Patients with Klippel-Trenaunay (KT) syndrome have a complex constellation of anomalies that includes cutaneous capillary malformation (usually on an affected limb), abnormal development of the deep and superficial veins, and limb asymmetry, usually enlargement. Mixed vascular malformations may be present and include capillary, venous, arterial, and lymphatic systems. The records of 79 patients referred for vascular anomalies were reviewed and 49 were found to have the three "cardinal" anomalies of KT syndrome. Twenty-six females and 23 males had 46 affected legs (27 right legs), 23 affected arms (15 right), 21 affected trunks, and 10 affected heads. Thirty-six had only one affected quadrant, 8 had two, and 5 had three or more. Although 40 patients had increased limb girth, measurable length discrepancy was noted in only 17 individuals. Patients were evaluated using a noninvasive imaging strategy including color duplex ultrasonography, MRI, lymphoscintigraphy, and plain radiographs. Treatment included compression, pulsed-dye laser treatment, reduction of arteriovenous malformations, and orthopedic procedures for overgrowth. All KT cases in this series occurred sporadically. We speculate that KT syndromes may be due to a somatic mutation for a factor critical to vasculogenesis and angiogenesis in embryonic development.