Background: Previous studies have shown an association between obesity and psychiatric disorders, primarily focusing on adults and the elderly. However, limited research has been conducted on students in this area. This study aimed to investigate the relationship between psychiatric disorders in students and obesity, as measured by body mass index (BMI). Materials and methods: This retrospective cross-sectional study utilized data from the Child and Adolescent Excellence Health Centre and the student care center at the Center of Excellence for Adolescent Health and Development, SS Hospital, IMS, BHU. A total of 7,548 students from both centers were enrolled between April 2018 and June 2022, of which 1,795 met the selection criteria and were included in the study. The final diagnosis of psychiatric disorders was based on the tenth revision of the International Statistical Classification of Diseases and Related Health Problems (ICD-10) diagnostic criteria for research (DCR) criteria. Obesity status was determined using BMI and waist circumference (WC). Double-tailed tests were employed to assess the correlation between age, BMI, gender, depression, and anxiety. Results: The mean age of the participants was 18.81 ± 4.01 years, with a majority being males (n = 931, 51.9%) compared to females (n = 864, 48.1%). Variables such as age (p < 0.001), marital status (p < 0.001), and education (p < 0.001) were significantly associated with BMI. A significant difference was observed in the mean BMI scores between participants with and without depression and anxiety. BMI showed a positive correlation with age, depression, and anxiety. Conclusion: Obesity appears to be associated with a higher likelihood of depression and anxiety among students compared to individuals with underweight or normal BMI.