- Consistent with the ‘‘scar hypothesis’’, according to which mood depression might impact personality, we examined the effect of unipolar and hypomanic mood disturbances on cluster B (i.e., narcissistic, histrionic, and borderline) personality disorder features. Data from 113 suicidal young adults were utilized, and cross-lagged associations between unipolar and hypomanic mood disturbances and cluster B personality disorder features were examined using manifest-variable structural equation modeling (SEM). Hypomanic symptoms predicted an increase in narcissistic and histrionic personality disorder features over the Time 1–Time 2 period, as well as an increase in narcissistic personality disorder features over the Time 1–Time 3 period. Unipolar depressive symptoms and borderline features were reciprocally and longitudinally associated, albeit at different time periods. The sample distinct features restrict generalization of the findings. An exclusive use of self-report measures might have contributed to shared method variance. Results are consistent with the notion that hypomanic symptoms increase narcissistic personality disorder tendencies. Depression and Anxiety 25:892–898, 2008. & 2007 Wiley-Liss, Inc.