Aims: Theory of Mind (ToM), a concept used to describe an individual's social cognitive abilities that play roles in social interaction, may have a significant role in explaining the clinical variables and social problems of affective disorders. This study aims to determine whether ToM functions are impaired in Bipolar Disorder (BD) compared to healthy controls as well as investigate the association between clinical variables of ToM deficit and social competence. Methods: A total of 50 patients diagnosed with BD who were in remission and 50 healthy control subjects were included in this crosssectional study. Demographic data and medical history of participants were assessed, and Beck Depression Inventory (BDI), Beck Anxiety Inventory (BAI), Eyes test, Hinting Task, Social Adaptation and Self-Evaluation Scale (SASS), Wechsler Adult Intelligence Scale-Revised (WAIS-R) tests were administered. Results: There were no significant differences with regards to age, gender and BDI scores between patient and control groups. Hinting test (P=0.001), Eyes test (P=0.001), SASS (P=0.007) and WAIS-R (P=0.001) scores were higher in the control group. There was a significant correlation between Hinting Test and WAIS-R (r=0.430, P=0.001), and between Eyes Test and age (r.-0.590, P=0.001), duration of bipolar disorder (r=-0.554, P=0.001), number of manic attacks (r=0.590, P=0.001) and WAIS-R (r=0.343, P=0.050). Logistic regression analysis showed that compared to the patient group, control group was related to Eyes test by 1.2-fold for each point increase in Eyes test (P=0.001) and 1.3-fold for each point increase in Hinting test (P=0.003). Conclusion: ToM deficit was an essential factor that separated BD patients in remission from healthy individuals. ToM deficit may play a role in the essential pathology or affect the presence, or even onset, of BD.