We conducted a descriptive study based on analysis of medical record reviews of a random sample of dehydration hospitalizations as well as hospital discharge files. The sampling frame for the medical record reviews included all of the hospitalizations between 1991 and 1995 (N = 28,047) for children (aged >1 month and <19 years) who were residents of Monroe County (Rochester), NY. No programs designed to replace pediatric hospitalizations were active or developing during the study period. Hospital discharge data were obtained from the Rochester hospitals' database, a data set developed and maintained cooperatively by all Rochester-area hospitals. Among these hospital discharges, there were 1121 with a primary diagnosis suggesting dehydration. Dehydration hospitalizations were identified by a primary hospital discharge diagnosis coded according to the International Classification of Diseases, Ninth Revision23 indicating gastroenteritis due to a specific agent, nonspecific viral gastroenteritis, noninfectious gastroenteritis or diarrhea, hypovolemia, or diarrhea. The following International Classification of Diseases codes falling in these clinical groups were encountered: 0030., 004.0, 004.3, 004.8, 004.9, 008.0, 008.00, 008.43, 008.45, 008.49, 008.5, 008.6, 008.61, 008.67, 008.69, 008.8, 009.0, 009.1, 276.5, and 558.9. Admissions with a primary hospital discharge diagnosis indicating vomiting alone (codes 787.0-787.03) were excluded for several reasons. The number of these vomiting hospitalizations (n = 16) was small compared with the number that met the definition of dehydration hospitalizations (1121). In our clinical experience, some children with simple, acute gastroenteritis manifest their illness primarily with vomiting at the time they are hospitalized, but before they are discharged from the hospital, they usually develop diarrhea as well; therefore, they receive a hospital discharge diagnosis of acute gastroenteritis. We believe that children who at hospital discharge have yet to develop illness manifestations that would support a diagnosis more specific than vomiting probably did not have acute gastroenteritis. They probably had an illness associated with a high level of diagnostic uncertainty, and thus might not make good candidates for care in alternative settings.