Investigations of individual differences that contribute to the severity of personality dysfunction are necessary for informing clinical best practices. This study examines the influence of two individual difference variables—quality of object relations (QOR) and psychological mindedness (PM)—on the severity of personality disorder (PD). Specifically, PM was investigated as a moderator of the impact of QOR on PD severity. The sample comprised 138 consecutively admitted outpatients participating in a partial hospitalization evening treatment program, all of whom presented with significant personality dysfunction. QOR emerged as having a significant effect on PD severity, which was significantly moderated by PM. Simple slopes analysis indicated that the association between low QOR (representing more dysfunctional object relations) and PD severity became less pronounced as PM increased from low to high, suggesting a compensatory effect of PM. Implications of the findings for understanding the development of severe PD and clinical practice are considered.