An 11-year-old girl presented with acute renal failure and severe hypertension. The blood film showed thrombocytopenia, numerous fragmented red blood cells, and a reticulocyte count of 10%. An intravenous pyelogram showed a small contracted left kidney, and plasma renin activity was increased in the left renal vein. Treatment with minoxidil and propranolol controlled the hypertension. After nephrectomy the hypertension resolved. Light microscopical examination of the left kidney showed a segmental renal hypoplasia. Malignant arterial hypertension can provoke a syndrome of haemolysis and uraemia in children. Aggressive lowering of blood pressure leads to an improvement in renal function.