Youth life satisfaction is a component of subjective well-being, an important part of a strengths-based approach to treatment. This study establishes the psychometric properties of the Brief Multidimensional Students' Life Satisfaction Scale-PTPB Version (BMSLSS-PTPB). The BMSLSS-PTPB showed evidence of construct validity with significant correlations as expected to measures of youth hope and youth symptom severity, and no relationship as expected to youth treatment outcome expectations. A longitudinal analysis was conducted examining the relationship between youth-reported life satisfaction and mental health symptom severity (youth-, caregiver-, and clinician-report) for 334 youth (aged 11-18 years) receiving in-home treatment. Results indicated that life satisfaction consistently increased over the course of treatment but increased faster in youth whose symptom severity, as rated by all reporters, decreased over the course of treatment. Implications, future directions, and limitations of the study are discussed.