The rationale for child and adolescent medical psychiatric units (CAMPUs) is given, primarily emphasizing differences from adult medical-psychiatry units. Results from a national survey describe the current status of CAMPUs in the continental United States. A total of 32 units were identified, with an additional 7 hospitals planning to establish a CAMPU. Levels of treatment intensity of CAMPUs were clarified, the general administrative structure of the 11 most treatment-intensive CAMPUs were described, and their combined patient populations are descriptively analyzed to present empirical data on the numbers and types of patients currently treated on such units.