Objective: Vaping is advertised as a method to mitigate weight gain after smoking cessation; however, while there is an established inverse association between conventional tobacco use and body mass index (BMI), there is little research on the relationship between e-cigarettes and BMI. This research tested whether e-cigarette use was associated with BMI. Methods: A secondary data analysis of 207,117 electronic medical records from the UAB was conducted. Patient data from 1 September 2017 through 1 June 2018 were extracted. To be included in the analysis, a patient's record had to include measures of e-cigarette use and key sociodemographic information. Ordinary least squares regression was used to test the association between e-cigarette use and BMI, controlling for covariates; unconditional quantile regression was used to determine whether the association varied by BMI quantile. For comparison with tobacco smoking, the association between current tobacco smoking and BMI was estimated in a sample from the same population. Results: Respondents in the sample had an average BMI of 30.8 and average age of 50.0 years when BMI was measured. The sample was 51% female, 49.7% white, 46.7% black, and 1.0% Hispanic; 16.4% of the sample had less than a college education and approximately 5% reported currently using e-cigarettes. Individuals who reported using e-cigarettes had, on average, a lower BMI compared to those who did not report currently using e-cigarettes; results indicated that this association did not significantly vary by BMI quantile. Individuals who reported being current smokers had a lower BMI, on average. Conclusion: These findings suggest that using e-cigarettes is associated with a lower BMI in a population of individuals seeking health care, consistent with the association between conventional tobacco use and BMI. This study is a springboard for future research investigating the associations between e-cigarette use, BMI, and risk of obesity in the general population.