Aim: To determine whether there are gender differences in prevalence of bipolar disorder and to describe differences in medical signs, symptoms and the course of the disease amongst women and men with bipolar disorder. Study design: Retrospective cohort study. Patients and methods: Data available from patient history was analysed. Patients with bipolar disorder hospitalised at the Psychiatric Clinic in KBC Osijek in the period from 2010 to 2015 were included in the study. The study included 121 patients with a diagnosed bipolar disorder, out of whom 39 (32.2%) were men and 82 (67.8%) were women. Results: Statistically significant differences were found concerning the age and marital status amongst male and female patients. Seven male patients (17.9%) and seven female patients (8.5%) attempted to commit suicide, whilst four male patients (10.3%) and one female patient (1.2%) repeated the suicide attempt; moreover, statistically significant difference was found in the second group. PTSD and schizoaffective disorders as comorbidities are more common in men while other psychiatric comorbidities are more common in women with bipolar disorder. Three female patients (6.8%) and no male patients had hypothyroidism in addition to bipolar disorder. Conclusion: The results of this study indicate a greater prevalence of bipolar disorder amongst women. Women suffering from bipolar disorder were on average 5 years older than men with bipolar disorder. The number of episodes of depression, mania, mixed and hypomanic episodes did not differ by gender. Significantly more men showed repeated suicidal behaviour. Women suffering from bipolar disorder are more prone to psychiatric comorbidities and they more frequently suffer from thyroid disease in the form of hypothyroidism.