Considerable improvements have been achieved in pediatric surgery during the last two decades: the mortality rate of neonates undergoing major operations has declined to less than 10%, and the morbidity of major operations has become negligible. This considerable improvement can be partly ascribed to a better understanding of the physiological changes that occur after an operation and to more appropriate management and nutrition of the critically ill and "stressed" neonates and children. The metabolic response to an operation is different in neonates from adults: there is a small increase in oxygen consumption and resting energy expenditure immediately after surgery with return to normal by 12-24 hours. The increase in resting energy expenditure is significantly greater in infants having a major operation than in those having a minor procedure. The limited increase in energy expenditure may be due to diversion of energy from growth to tissue repair. During parenteral nutrition, it is not advisable to administer more than 18 g/kg/day of carbohydrate because this intake will be associated with lipogenesis, increased CO(2) production, and increased free radical-mediated lipid peroxide formation. Glutamine intake is potentially beneficial during total parenteral nutrition, although a large, randomized, controlled trial in surgical neonates requiring parenteral nutrition is needed to provide evidence for its benefit.