Background and aims: Recent evidence showed significant rate of anxiety co-morbidity in patients with a diagnosed bipolar disorder. In this research we tried to study the rate of bipolar spectrum disorder (soft bipolarity) in those who are treating with anxiety disorder diagnosis. Methods: In this descriptive-analytic study, 210 patients with a diagnosed anxiety disorder were selected from out patient's clinics and clinic of Noor general hospital in Isfahan (Iran). 210 persons from general population were selected as control. Bipolar spectrum diagnostic scale (BSDS) was used as screening tool of bipolar disorder. Data were analyzed using X square and logistic regression. Results: Considering the homologizing between 2 groups, there was no significant difference regarding age, genders and educational level between 2 groups. Bipolar spectrum disorder was 15.8% in patients with anxiety disorders (case group) and 5.4% in the control group (P<0.001, OR=3.38, CI95%=1.65-6.94). This finding means that the probability of bipolar spectrum disorder in patients with anxiety disorders was about 3 times the control group. Conclusion: Co-morbidity of bipolar spectrum disorder (soft bipolarity) is significantly more prevalent in those with a diagnosed anxiety disorders than control group and needs to be considered in prognostication and treatment of the patients with anxiety disorder
