Individuation is widely considered a fundamental developmental task of adolescence. It is a process through which the adolescent seeks to define new boundaries between his or her self and others, and the failure to do so has been shown to have serious consequences. Given its importance for understanding developmental transitions, it is surprising that there are few assessments of dysfunctional individuation. Over three studies, we provide evidence of a promising new measure of this important construct: the 10-item Dysfunctional Individuation Scale (DIS). Using confirmatory factor analysis and item response theory, we demonstrate that the DIS possesses a strong one-factor structure and excellent psychometric properties. Furthermore, we document the convergent, discriminant, and concurrent validity of the DIS through its relationships with indices of individuation, adjustment, and clinically relevant symptoms. Finally, we examine the incremental validity of the DIS over neuroticism as a predictor of depression (Beck Depression Inventory-II). [ABSTRACT FROM AUTHOR]