The aim of the study was to assess the incidence, causes, diagnostic and treatment modalities, and outcome of vascular thrombosis after kidney transplantation in children. Between 1984 and 1995 we performed 176 kidney transplants in pediatric recipients aged 1 to 18 years. Vascular thrombosis followed 7 transplants, 4 were renal vein and 3 arterial thromboses. Venous thromboses occurred 2 to 12 days after transplantation. All of the patients with a renal vein thrombosis lost their grafts. Arterial thrombosis developed in 2 cases of double renal arteries which were separately anastomosed into the recipient vessels. One graft was lost, but the other was saved by thrombolytic therapy (streptokinase). One child experienced intrarenal segmental artery thrombosis during acute vascular rejection, which resolved following combined anti-rejection and thrombolytic (intra-arterial streptokinase) treatment with full recovery of graft function. In all, vascular thrombosis complicated 7 out of 176 transplants (4.0%), and was the cause of 5 graft losses (2.8%). The incidence of vascular thrombosis was not increased in grafts with vascular anomalies (3/34 v. 4/142; p>0.05, chi sq.). We conclude that acute tubular necrosis, rejection and unstable volemia may predispose to vascular thrombosis. In selected cases, early diagnosis of vascular thrombosis may enable graft salvage by surgical or thrombolytic treatment.