Introduction: Acne vulgaris is a common skin disorder that affects 79% to 95% of the young population. In United States, 40% to 45% of men and women older than 25 years of age have some degrees of facial acne that continues to the middle age in 12% of women and 3% of men. Acne vulgaris (acne) is one of the most common chronic dermatological diseases among adolescents, affecting about 80% of young people between 12 and 18 years of age. Obesity is one of the biggest problems in western life style but nowadays, the problem is increasing even in low and middle-income countries. Body Mass Index (BMI) is used to accurately measure obesity. Objective: To find out the association between different categories of BMI and severity of acne. Materials and Methods: This was a cross sectional prospective study conducted in the outpatient Department of Dermatology, Shaheed M. Monsur Ali Medical College Hospital, Sirajganj, Bangladesh from January to March 2022. All the newly diagnosed patients with acne were included in the study. Height and weight of the patients was recorded and BMI was calculated. BMI was categorized as underweight, normal weight, overweight and obese. Type of lesions were noted and severity of acne was graded from 1 to 4. Statistical analysis was performed using SPSS version 21 for windows. One-way Analysis of Variance between groups (ANOVA) test was applied. P value of less than 0.05 was considered significant. Results: A total of 125 patients with acne were included in the study. Age of the patients ranged from 10 to 50 years with mean age of 20.82 ±5.9 years. Most of the patients were in the age group of 11-20 years. There was slightly a female preponderance with female: male ratio of 1:1.4. According to BMI, 65.5% were normal, 12% were overweight, 20.5% were underweight and 2% of patients were obese. Majority of the patients had Grade 2 acne (52.8%). There was no significant association between the BMI and severity of acne (p=0.129). Maximum number of obese patients had grade 4 acne, maximum number of overweight patients had grade 2 acne and maximum number of underweight patients had grade 1 acne. But there was no significant association between the BMI categories and grades of acne (p=0.129). Similarly, there was no significant association between the age and grades of acne (p=0.61). Conclusion: The prevalence of acne with severity more than moderate was much lower in patients who were underweight (BMI less than 18.5). However, this study showed no statistically significant difference in BMI among people with different severities of acne. Population-based studies, as well as age restriction of the participants, can lead to more accurate and reliable results in this regard. There was no significant association between BMI and severity of acne. However, a larger population-based study is indicated to validate our finding.