The spectrum and outcome of acute renal failure (ARF) were studied in 205 children aged between 1 month and 12 yr. There were 145 boys and 60 girls; 23 per cent were below 1 yr and 49 per cent between 1 and 4 yr. The main causes of ARF were haemolytic uraemic syndrome (HUS) in 36 per cent, serious infections in 19 per cent, acute gastroenteritis and dysentery in 17 per cent, glomerulonephritis (GN) in 13 per cent and intravascular haemolysis (IVH) in 6 per cent. Most patients with HUS, serious infections and gastroenteritis were below 5 yr, whereas GN and IVH occurred in older children. HUS was mostly associated with dysentery; Shigella and several other pathogens were isolated from stools in 35 per cent. In most patients with HUS disseminated intravascular coagulation and renal cortical necrosis were present, with a high mortality. The outcome was also poor in infants with serious infections. IVH occurred in patients with G-6-PD deficiency. In such patients and in those with post-streptococcal GN the prognosis was good. Crescentic GN had a poor outcome. Our observations highlight the common and serious nature of ARF in India. However, most of the underlying causes are preventable.