<b><i>Background:</i></b> It is widely established that personality disorder has as broad negative impact on psychotherapy outcomes. Given the increased emphasis on dimensional traits for personality pathology in the DSM-5 and the proposal for the ICD-11, it is important to understand how traits are linked to treatment outcomes. Building on past research with general traits, we hypothesized that more nuanced and specific relations would be apparent. Furthermore, much of the past research has relied upon self-reports of personality and little is known about how ratings from therapists might be related to outcomes. <b><i>Sampling and Methods:</i></b> The present paper examined how dimensional traits from the Five-Factor Model predicted outcomes in a case series of 54 therapist-client dyads within a doctoral training clinic. Importantly, this extends past research as dimensional traits were rated by both therapists and clients at intake as well as sequentially over the course of therapy. <b><i>Results:</i></b> Correlations and regression analyses indicated that traits predicted a variety of outcomes including initial engagement in treatment as well as overall symptom reduction across therapy. Specifically, preliminary evidence suggests that therapist-rated conscientiousness at intake was positively related to clients’ early engagement in therapy. In addition, openness to experience after the 4th session – particularly as rated by the client – was predictive of long-term therapy outcomes. <b><i>Conclusions:</i></b> Broadly, these results provided preliminary information about the promise of dimensional models for improving the clinical utility of personality disorder diagnoses. More specifically, these results reinforced the relevance of personality assessment during therapy and indicated the potential predictive value of ratings by therapists and their clients.