The prevalence of obesity is increasing worldwide, resulting in various health issues such as hypertension, dyslipidemia, diabetes mellitus, heart disease, and a lower life expectancy. Importantly, several psychiatric disorders and the use of psychotropic medications have been linked to obesity, and the possible risk factors need further investigation. This study examined the prevalence of obesity and its associated factors using a self‐administered questionnaire. Participants were recruited from three outpatient clinics and individuals who met one or more of the ICD‐10 F0‐F9, G4 diagnoses were included. In total, 1384 participants completed the questionnaire about their lifestyle. Statistical analysis compared the demographic and clinical characteristics of the individuals who were obese (Body Mass Index: BMI ≥25) and those who were non‐obese (BMI <25). The results revealed that the factors associated with obesity in psychiatric outpatients were being male, prolonged treatment duration, eating out frequently, and use of both second‐ and first‐generation antipsychotics. The study emphasized the importance of closely monitoring BMI in individuals with multiple obesity‐related factors.