The current study looks to evaluate the validity and reliability of a brief measure of overall functioning for adolescents. Clinicians were asked to complete the Overall Functioning Scale for 72 adolescents consecutively admitted to the adolescent psychiatric inpatient service of a community safety net medical center. The results revealed that this new measure is related to the patients’ length of stay, clinician-rated measures of social cognition and object relations, Global Assessment of Functioning score at admission, and global rating of engagement in individual psychotherapy. Results also showed that the OFS was related to patients’ history of non-suicidal self-harm as well as treatment outcome as assessed by measures of psychological health and well-being and symtomatology. Hierarchical regressions reveal that the OFS shows incremental validity above the admission GAF score in predicting length of stay. The results also showed that the OFS demonstrates inter-rater reliability in the excellent range (ICC 1,2) of .88. Clinical implications of the use of this tool as well as areas of future research are discussed.