Objective: We aimed to investigate the prevalence of the metabolic syndrome (MetS) and its individual components in subjects with bipolar disorder (BD) compared to those with major depressive disorder (MDD) and non-psychiatric controls. Methods: We examined 2431 participants (mean age 44.3. ±. 13.0, 66.1% female), of whom 241 had BD; 1648 had MDD; and 542 were non-psychiatric controls. The MetS was ascertained according to NCEP ATP III criteria. Multivariable analyses were adjusted for age, sex, ethnicity, level of education, smoking status and severity of depressive symptoms, and in the case of BD subjects, also for psychotropic medication use. Results: Subjects with BD had a significantly higher prevalence of MetS when compared to subjects with MDD and non-psychiatric controls (28.4% vs. 20.2% and 16.5%, respectively, p<. 0.001), also when adjusted for sociodemographic and lifestyle factors (OR 1.52, 95% CI: 1.09-2.12, p= 0.02 compared to MDD; OR 1.79, 95% CI: 1.20-2.67, p= 0.005 compared to non-psychiatric controls). The differences between BD subjects with controls could partly be ascribed to a higher mean waist circumference (91.0. cm vs. 88.8, respectively, p= 0.03). In stratified analysis, the differences in the prevalence of MetS between patients with BD and MDD were found in symptomatic but not in asymptomatic cases. Conclusion: This study confirms a higher prevalence of MetS in patients with BD compared to both MDD patients and controls. Specifically at risk are patients with a higher depression score and abdominal obesity.