Background: Bipolar affective disorder may be associated with alterations in thyroid function. A comprehensive thyroid assessment is important for assessing clinical and sub-clinical imbalances linked to a variety of mood disorders like bipolar affective disorder. Aim: To find out the association between bipolar affective disorder and thyroid dysfunction. Materials and method: The present cross-sectional study was conducted at Government District Wenlock Hospital, Mangalore (GDWH), India. A total of 50 newly diagnosed bipolar affective disorder patients and 50 age and sex matched controls without bipolar affective disorder as confirmed by the application of Bipolar Spectrum Diagnostic Scale were included in the study. Thyroid function was assessed among the patients and control group to study the association between bipolar affective disorder and thyroid dysfunction. Odds ratio was calculated to find out the strength of association between thyroid gland dysfunction and bipolar affective disorder. Results: The mean Bipolar Spectrum Diagnostic Scale score among patients diagnosed with bipolar affective disorder was 20.84 and that of the control group was 1.98. The proportion of thyroid dysfunction among bipolar affective disorder patients and among control group was 14% and 6% respectively. The odds ratio was calculated to be 2.55. Mean T3 values were higher in the bipolar affective disorder patients than the control group and this association was found to be statistically significant (p=0.031). Mean T4 and TSH values were higher among the bipolar affective disorder patients but did not show any significant differences when compared with the control group. Conclusion: The present study concludes that a statistically significant association exists between elevated T3 hormone and bipolar affective disorder and observes that the patients with bipolar affective disorder are 2.55 times more commonly associated with thyroid dysfunction. © 2012 Elsevier B.V.