This is the first multisite, prospective study of behavioral and mental health disorders of youth in residential treatment centers (RTC) and therapeutic foster care (TFC), and the first study to compare the two. This study addressed two questions in a sample of 22 agencies in 13 states: (1) how prevalent were emotional and behavioral disorders in the youth admitted to RTCs and TFC?, and (2) were the youth in RTCs significantly more likely to be disturbed than youth served in TFCs? Data were drawn from the Time 1 phase of the longitudinal national "Odyssey Project" developed by the Child Welfare League of America (1995). Measures included an extensive child and family characteristics form (CFC) and the Child Behavior Checklist (CBCL). The results revealed extremely high levels of behavioral and mental health disorders in the sample as a whole, well above the norms for a non-child welfare population. The prevalence of disorder in the RTC population was substantially greater than in the TFC population. (Contains 3 tables and 4 footnotes.)