Clinical features and management of 47 children with Klippel-Trenaunay syndrome treated since 1970 were reviewed. Haemangiomas and soft tissue and/or skeletal hypertrophy were present in all 47 patients; venous varicosities developed in 37 (79 per cent). There was no clinical evidence of macrofistulous arteriovenous communications in any patient. Thromboembolic episodes occurred in five children (11 per cent) and 25 (53 per cent) experienced thrombophlebitis. The Kasabach-Merritt syndrome was observed in 21 (45 per cent) and six (13 per cent) presented with high-output cardiac failure. Other manifestations included haematuria in five (11 per cent), rectal or colonic haemorrhage in six (13 per cent), and vaginal, vulval or penile bleeding in six (13 per cent) children with visceral and pelvic haemangiomas. In 26 patients (55 per cent) symptomatic treatment only was required. Surgery was undertaken in selected cases for complications of the haemangioma, for cosmetic reasons and for chronic venous insufficiency. Only one of four children who underwent resection of varicose veins improved. There was no death, but significant morbidity was associated with the treatment of Kasabach-Merritt syndrome and high-output cardiac failure.