Medical professionals are now relying on social media platforms like Twitter to express their recommendations for the use or avoidance of products like electronic cigarettes (e-cigs), which may have long-term health consequences for users. The goal of this study is to compare how physicians from the United States and the United Kingdom talk about e-cigs on Twitter and identify the topics that these groups perceive as salient. Comparing tweets from the U.S. and U.K. will allow for a better understanding of how medical professionals from these countries differ in their attitudes toward e-cigs. This information can be also used to inform policies designed to regulate the use of e-cigs. Using a text-mining program, we analyzed approximately 3,800 original tweets sent by physicians from the U.S. and the U.K. within a 1-year time span (June 2015 through June 2016). The program clustered the tweets by topics, which allowed us to categorize the topics by importance. Both sets of tweets contained debates about the degree to which e-cigs pose a threat to health, but the U.S. tweets emphasized the dangers of e-cig use for teens, while the U.K. tweets focused more on the potential that e-cigs have to be used as a smoking cessation aid. Doctors are using Twitter to share timely information about the potential risks, benefits, and regulations associated with e-cigs. Evaluating these tweets allows researchers to collect information about topics that doctors find important and make comparisons about how medical professionals from the U.S. and the U.K. regard e-cigs.