Background: Acne vulgaris is a common skin disorder that affects 79% to 95% of the young population. Some studies have focused on the role of overweight and obesity in initiation and exacerbation of acne. This study investigated the relationship between BMI and the severity of acne. Method: This cross-sectional study was conducted on 107 acne patients. One form was completed for each patient with regard to demographic characteristics including age, sex, weight, height, BMI, and also the severity of acne based on the Global Acne Severity Scale (GEA Scale), duration of the disease, type of medication, smoking history, duration of exposure to sunlight and intake of dairy products and chocolate. Result: In this study, 93 patients (86.9%) were female and 14 patients (13.1%) were male, with a mean age of 22.5 years. The mean BMI of the participants was 23.36 kg/m2 . With regard to acne severity groups, the moderate acne group had the highest frequency in total (37.4%). The highest mean BMI was seen in the very severe acne group (24.4 kg/m2 ), and the lowest mean BMI was observed in the severe acne group (21.86 kg/m2 ). There was no significant correlation between the acne severity and BMI (p=0.806).The mean disease duration was 4.13 years, which was not significantly associated with BMI. There was no significant association between the type of medical therapy and BMI. 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.