During the last 15 years, medical care of the acutely ill infant, child, and adolescent has become increasingly complex. The system whereby a child's outpatient pediatrician would care for the patient's acute medical illness has mostly disappeared. Children of all ages with the vast majority of acute illnesses once treated as inpatients are now managed almost exclusively in the outpatient setting. The nature of inpatient care, whether on the intensive care unit or on the ward, has changed gradually but inexorably to multidisciplinary care for children with acute exacerbations of complex chronic conditions and brief hospitalizations for otherwise well children with the most severe presentations of common acute illnesses.