Objective: To determine the impact of the personality traits neuroticism and extraversion as well as comorbid personality disorders on the rate of remission, recurrence, and conversion to bipolar disorder after the first lifetime episode of depression.

Methods: A total of 301 inpatients or outpatients aged 18–70 years with a validated diagnosis of a single depressive episode according to ICD-10 were assessed by the Structured Clinical Interview for DSM-IV Axis II Personality Disorders and the Eysenck Personality Questionnaire from 2005 through 2007. At 5-year follow-up, 262 patients were reassessed by means of the Life Chart Method and diagnostic interviews from 2011 through 2013. Cox regression analyses were used to estimate the effect of personality factors on the rates of remission, recurrence, and conversion to bipolar disorder, respectively.

Results: A comorbid cluster C personality disorder decreased the rate of remission by 30% (HR = 0.7; 95% CI, 0.5–0.9; P = .02) and increased the rate of recurrence after remission of the first depression by 80% (HR = 1.8; 95% CI, 1.0–3.0; P = .04). A higher neuroticism score at baseline decreased the rate of remission by 20% for each increase of 1 SD (HR = 0.8; 95% CI, 0.7–0.9; P = .002), and a higher level of extraversion increased the rate of conversion to bipolar disorder by 60% for each increase of 1 SD (HR = 1.6; 95% CI, 1.0–2.5; P = .05).

Conclusions: Comorbidity of cluster C personality disorders and the level of neuroticism and extraversion have significant impact on the long-term prognosis of depression. The identified predictors of the course of illness should guide patients and clinicians for individualized tailored treatment of comorbid conditions in depression.