In a series of 859 transplantations performed in children and adolescents from January 1973 to December 1992, vascular thrombosis accounted for 18% of all graft losses (2nd cause of graft failure), and 57% of early failures (within 2 months). Renal veins and arteries were equally affected. The young age of the donors and recipients constituted the main risk factor, thrombosis accounting for 40 and 37% respectively of all graft losses in donors and recipients <5 years old. This explained the lower survival rate of these age groups after grafting, as reported in most published pediatric series. The prophylactis use of a low molecular weight heparin in high-risk grafts may help to decrease its incidence. A renal artery stenosis, located a few cm beyond the anastomosis in 2/3 of cases, was observed in 10% of grafts. Often severe hypertension (HBP) with cerebral complications, responsible for permanent sequelae in some cases, was the prominent symptom. Anti-hypertensive drug therapy was sufficient to control HBP in 40 cases out of 72, and in 10 of these, a spontaneous regression of the stenosis was remarked within a few months after repeated angiography. Transluminal angioplasty was used on 26 stenosis and was effective in 2/3 of cases; the recurrence rate, however, was 27%.