The association of nutritional depletions with physiologic instability and quantity of care was examined in 60 critically ill children. Nutritional status was evaluated by anthropometric techniques. Physiologic stability was measured by the Physiologic Stability Index and quantity of care was measured by the Therapeutic Intervention Scoring System. Acute protein-energy malnutrition was significantly associated with increased physiologic instability and increased quantity of care (p less than 0.01). This association was present for the total group, children less than 24 months of age, and for these two groups with nonsurvivors excluded. Mortality was also significantly associated with acute protein-energy malnutrition (p less than 0.001). Physiologic instability and increased quantity of care were not associated with chronic protein-energy malnutrition, fat store depletion, or somatic protein store depletion. We conclude that acute protein-energy malnutrition in critically ill children is associated with increased physiologic instability and increased quantity of care.