ABSTRACT: Importance:Millions of Americans use electronic cigarettes (e-cigarettes). A growing number of state and local governments have started to draft and implement laws regarding the sale, marketing, and use of e-cigarettes. The association of US state regulations regarding e-cigarettes with e-cigarette use remains unknown. Objective:To examine the association of US state regulations regarding e-cigarettes with current e-cigarette use among adults in the United States. Design, Setting, and Participants:This cross-sectional study included adults aged 18 years or older from the 2016 and 2017 Behavioral Risk Factor Surveillance System, which is a nationwide, telephone-administered survey that collects state-representative data on health-related risk behaviors, chronic health conditions, and use of preventive services. Data analysis was performed from February 1, 2019, to April 31, 2019. Exposures:United States state laws regulating e-cigarette use, including prohibiting e-cigarette use in indoor areas of private workplaces, restaurants, and bars; requiring retailers to purchase a license to sell e-cigarettes; prohibiting self-service displays of e-cigarettes; prohibiting sales of tobacco products, including e-cigarettes, to persons younger than 21 years; and e-cigarette taxes. Main Outcomes and Measures:Current use of e-cigarettes. Results:Among 894?997 participants aged 18 years or older (503?688 women [51.3%], 679?443 non-Hispanic white [62.6%], 71?730 non-Hispanic black [16.3%], 69?823 Hispanic [11.4%], and 74?001 non-Hispanic other races [9.8%]), 28?907 (weighted prevalence, 4.4%) were currently using e-cigarettes. The age-standardized weighted prevalence of current e-cigarette use varied across US states and territories, from 1.0% in Puerto Rico to 6.2% in Guam. After adjustment for demographic, socioeconomic, and lifestyle factors, including conventional cigarette use, the odds ratios of current e-cigarette use were 0.90 (95% CI, 0.83-0.98) for state laws prohibiting e-cigarette use in indoor areas of private workplaces, restaurants, and bars; 0.90 (95% CI, 0.85-0.95) for state laws requiring retailers to purchase a license to sell e-cigarettes; 1.04 (95% CI, 0.99-1.09) for state laws prohibiting self-service displays of e-cigarettes; 0.86 (95% CI, 0.74-0.99) for state laws prohibiting sales of tobacco products, including e-cigarettes, to persons younger than 21 years; and 0.89 (95% CI, 0.83-0.96) for state laws applying taxes to e-cigarettes. Conclusions and Relevance:These findings suggest that several state regulations regarding e-cigarettes may be associated with reduced e-cigarette use among US adults.