Background
The aim of the study was to investigate whether patients with bipolar disorder (BD) in remission differ in personality traits compared with a healthy control group.

Methods
A sample of patients with BD (n = 44) was compared with an individually matched control group (n = 44) using the Danish version of the Revised NEO Personality Inventory (NEO PI-R). Paired t-tests were used to analyze differences between the two groups and multiple regression models to evaluate predictors of NEO scores in the patient group.

Results
Patients with BD reported significantly higher scores on both Neuroticism and Openness to Experience and lower scores on Conscientiousness. No differences were found on Extraversion and Agreeableness. The effect size for Neuroticism and its facets had a range from 0.77 to 1.45 SD.

Statistically significant group differences were seen on 15 of 30 lower-level traits within all five high-order dimensions. There were large effect sizes for Trust (0.77) and Self-discipline (0.85), while the other statistically significant group differences were smaller with effect sizes in the range from 0.43 to 0.74 SD.

However, patients with BD showed a profile with high-order dimensions and lower-level traits within one standard deviation from the mean score except for the lower-level trait Depression.

Conclusions
Our findings suggest that patients with BD differ from healthy control persons with respect to higher levels of Neuroticism, Openness to Experience and lower scores on Agreeableness and on Conscientiousness, but prospective studies are needed to evaluate the implications of this finding.