The goal of this article was to develop and validate a self-complexity scale for adolescents. Therefore, 4 empirical studies were developed. In Study 1, a content analysis of attributes used in school books was conducted. This analysis was complemented in Study 2 with an exploratory study of adolescent's self-descriptions in an open-ended questionnaire (N = 67). From this, a set of 42 attributes were identified. In Study 3, attributes' relevance and valence was evaluated by 109 adolescents, and a final set of 32 attributes was identified for the new scale. In Study 4, the Self-Complexity Scale for Adolescents (SCSA) was administered to a sample of 174 adolescents (aged 12–16), and SCSA structure, psychometric properties and correlation with self-esteem, as well as age and gender differences were analyzed. The research findings suggest that SC is a bidimensional construct and that SCSA is a reliable instrument. Furthermore, negative correlations were found between total and negative SC and self-esteem scores (convergent validity). Age differences were found in negative SC scores, with adolescents aged 14–16 exhibiting higher scores than 12- to 14-year-olds.