Aim. Mixed episodes (MS) and rapid cycling (RC) belong to severe and destabilizing features of the bipolar affective disorder (BD) and make serious risk factors for suicide and poor long-term prognosis. Personality may determine the course and clinical expression of mood disorders. The objective of this study was to assess the personality traits in patients with or without mixed state (MS) and with and without rapid cycling (RC). Material and methods. 108 euthymic bipolar patients (32 with MS and 28 with RC) were assessed with the use of NEO - five-factor inventory (NEO-FFI). Ratings were correlated with the clinical data of the course of BD. Results. Neuroticism was found to be significantly higher in patients with MS as compared to those without MS history. No difference in personality measures was revealed between patients with or without RC. Limitations. The results are limited mainly by the relatively small sample size, and also by the lack of control group of healthy individuals. It would be good to test the conclusions in other institutions. Conclusions. The results obtained suggest that high neuroticism in bipolar patients, measured by NEO-FFI, may be associated with a predisposition to mixed state but not to rapid cycling.