Background: Adults with body image dissatisfaction (BID) are more likely to be depressed, anxious, and suicidal when compared to those without intense dissatisfaction over their appearance. The current study aimed to estimate the prevalence and factors associated with BID among out-patients with mental illness in Singapore. Methods: Data was collected from 310 psychiatric out-patients using a self-administered questionnaire. Measurements used were socio-demographic characteristics, Body Mass Index scores, Body Shape Questionnaire, Binge Eating Scale, Eating Attitudes Test, Beck’s Depression Inventory, Beck’s Anxiety Inventory and Alcohol Use Disorders Identification Test. Results: A prevalence of 30.9% of BID was established among psychiatric out-patients in Singapore. Being female, having higher BMI scores, binge eating behavior, eating disorders, and those diagnosed with depression were positively associated with BID. Conclusion: BID is prevalent among those with psychiatric illnesses which could lead to a higher degree of psychological distress and the emergence of eating disorders.