This paper reviews maladaptive trait development (DSM-5 Section III Criterion B), the development of DSM-5 Section II borderline personality disorder, and research on the development of identity, self-direction, empathy/mentalizing, and intimacy (DSM-5 Section III Criterion A). Combined, these previously disparate literatures begin to point to an integrated developmental theory of personality pathology, which suggests that Criterion A concepts (identity, self-direction, empathy, and intimacy) coalesce around the development of self, marking a discontinuous (qualitative) developmental shift. This developmental shift is a function of the demands placed on individuals to take on independent adult role function, combined with biologically-based maturational cognitive and emotional advances during adolescence. Section II personality disorder ensues when an integrated and coherent sense of self fails to develop, resulting in nonfulfilment of adult role function. In this sense, Criterion A self function can account for the onset of Section II personality disorder in adolescence, while Criterion B provides a useful descriptive account of continuous aspects of personality function over time.