Objective: The primary aims of the study were to examine the reliability and validity of the Health of the Nation Outcome Scales for Children and Adolescents (HoNOSCA) in a sample of adolescents requiring medium to long-term in-patient psychiatric treatment and to examine the association between HoNOSCA scores and age, gender and length of treatment. Methods: A multidisciplinary team completed the HoNOSCA for 51 adolescent patients at intake and at 3- and 6-months following admission to the unit. Results: The study provided support for the test-retest reliability, concurrent and convergent validity, but not the internal reliability, of the HoNOSCA. Total HoNOSCA scores at intake were similar to those found in adolescent outpatient samples, although there were some differences at the level of individual items. Similarly, while the total HoNOSCA score showed some sensitivity to change, using the total HoNOSCA score obscured important changes in specific domains of functioning over the course of admission. Conclusion: The HoNOSCA was found to be a valid measure of global functioning at intake, thereby supporting its use in an adolescent psychiatric unit. However, focusing on individual items, rather than total score, appears more useful in evaluating the impact of inpatient psychiatric treatment on adolescents.