Using exploratory structural equation modeling and multiple regression, we examined the factor structure and criterion relations of the primary scales of the Inventory of Personality Organization (IPO; Kernberg & Clarkin, 1995) in a nonclinical sample. Participants (N = 1,260) completed the IPO and measures of self-concept clarity, defenses, affect and emotion regulation, and risky and self-injurious behavior. In contrast to that of Lenzenweger, Clarkin, Kernberg, and Foelsch (2001), a 4-factor measurement model was derived with factors representing instability of sense of self and other, instability of goals, instability of behaviors, and psychosis. The 1st of these factors related most strongly to external measures of self-concept clarity, defenses, and affect, whereas the 3rd factor related most strongly to measures of risky behavior and self-injury. These results suggest that the IPO's factor structure does not conform to the hypothesized 3-factor model, although it does capture important elements of Kernberg's (1996) theory of personality organization, especially the central construct of representations of self and others. The results point to several areas in which the IPO might be refined to provide a more comprehensive and theoretically appropriate measure of the borderline personality organization construct. (Contains 2 tables, 1 figure, and 1 footnote.)