We observed 12 boys and 1 girl, 5-15 years old, presenting with acute renal failure (ARF) and severe hypertension. They constituted 4.9% of all patients with ARF. There was no preceding diarrheal or respiratory prodrome. Clinical and laboratory findings were indicative of hemolytic uremic syndrome (HUS) in 4, but obscure in 9 others. Renal biopsies revealed variably severe occlusive thrombotic microangiopathy (TMA) affecting predominantly interlobular arteries in 8 and both arteries and glomeruli in 5 cases. Glomerular crescents and cortical necrosis were not seen. Following supportive therapy, 8 progressed to or died of uremia; 2 showed persistent proteinuria, 1 moderate hypertension and 2 complete recovery. Our observations indicate that renal TMA without a prodromal illness and typical features of HUS may present with ARF, proteinuria and severe hypertension, and is associated with high mortality.