Familial paroxysmal rhabdomyolysis with myoglobinuria is a rare and life-threatening disease of young children, of unknown aetiology. Attacks bear no relation to exercise, are usually triggered by intercurrent infections and are often severe. The authors describe two cases and suggest plans for the prevention and management of attacks. Fasting appears to be the crucial factor precipitating attacks, but is not associated with hypoglycaemia or with a defect in lactate production, ketogenesis or fatty acid mobilisation. The fatty acid-binding protein in a muscle biopsy from one case was normal.