Purpose: Everyday functioning is an important outcome for studies of the developmental psychopathology of adolescence. An unbiased, well-validated, and easy-to-use instrument to specifically assess normal adolescent functioning is not yet available. The current study aimed to introduce and validate the Multidimensional Adolescent Functioning Scale (MAFS). Methods: The MAFS was developed by clinical consensus, resulting in a 23-item self-report questionnaire with three distinct subscales: general functioning, family-related functioning, and peer-related functioning. MAFS data were collected in a general population sample (N = 842; mean age = 15.0 years [standard deviation =.4]) at baseline and again at 1- and 3-year follow-up. Psychometric analyses included confirmatory factor analysis, calculations of internal consistency, scale correlations, and correlations with the abridged General Health Questionnaire. Results: Confirmatory factor analysis showed that the hypothesized 3-factor structure fits well to the MAFS data. All scales showed adequate internal consistency (greatest lower bound:.75-.91) and sufficient discriminative ability (scale intercorrelations: ρ =.15-.52). Of the scales, general functioning was most strongly correlated with the General Health Questionnaire, whereas family- and peer-related functioning showed weaker correlations with this general measure. The results were stable across repeated measurements and gender groups. Conclusions: The MAFS is an easy-to-use instrument with good psychometric characteristics, which could be suitable for a broad range of future research applications, especially when a multidimensional and unbiased indication of normal adolescent functioning is required.