鈥� A total of 403 multiple diagnoses were independently assigned to 41 patient protocols by 73 psychiatrists, psychologists, and social workers to determine the levels of interrater reliability of the Group for the Advancement of Psychiatry (GAP) diagnostic categories. With the exception of the psychotic disorders category, these diagnostic categories were found to have low levels of interdiagnostician reliability. Differences in the reliabilities across disciplines and levels of training were found. It is noted, however, that neither years of experience, kind of training, nor direct contact with the patient can be regarded as a substitute for improvements in the classification system itself. The importance of a reliable classification system for child psychiatry is emphasized and suggestions for improvements in the present GAP system are made.