The incidence of acute renal failure in children is higher due to the prevalence of diarrheal dehydration, use of nephrotoxic substances and sepsis. The occurrence in the newborn has increased, probably due to the large number of seriously sick infants maintained in neonatal intensive care units. Various laboratory examinations have been proposed as diagnostic indices of acute renal failure in children. Among these are the urine-to-plasma concentrations of urea and creatinine and the urine-to-plasma osmolality ratio. The fractional excretion of sodium and the so-called renal failure index are the most reliable of the diagnostic tests. The functional abnormalities and complications of acute renal failure include reduced glomerular filtration rate, retention of nitrogenous wastes, hyponatremia, hyperkalemia, metabolic acidosis, hypocalcemia, hyperphosphatemia and hypermagnesemia. The principles of management and treatment of complications are discussed.