BACKGROUND: Given that continued smoking after a cancer diagnosis increases the risk of adverse health outcomes, patients with cancer are strongly advised to quit. Despite a current lack of evidence regarding their safety and effectiveness as a cessation tool, electronic cigarettes (E‐cigarettes) are becoming increasingly popular. To guide oncologists' communication with their patients about E‐cigarette use, this article provides what to the authors' knowledge is the first published clinical data regarding E‐cigarette use and cessation outcomes among patients with cancer.METHODS: A total of 1074 participants included smokers (patients with cancer) who recently enrolled in a tobacco treatment program at a comprehensive cancer center. Standard demographic, tobacco use history, and follow‐up cessation outcomes were assessed.RESULTS: A 3‐fold increase in E‐cigarette use was observed from 2012 to 2013 (10.6% vs 38.5%). E‐cigarette users were more nicotine dependent than nonusers, had more prior quit attempts, and were more likely to be diagnosed with thoracic and head or neck cancers. Using a complete case analysis, E‐cigarette users were as likely to be smoking at the time of follow‐up as nonusers (odds ratio, 1.0; 95% confidence interval, 0.5‐1.7). Using an intention‐to‐treat analysis, E‐cigarette users were twice as likely to be smoking at the time of follow‐up as nonusers (odds ratio, 2.0; 95% confidence interval, 1.2‐3.3).CONCLUSIONS: The high rate of E‐cigarette use observed is consistent with recent articles highlighting increased E‐cigarette use in the general population. The current longitudinal findings raise doubts concerning the usefulness of E‐cigarettes for facilitating smoking cessation among patients with cancer. Further research is needed to evaluate the safety and efficacy of E‐cigarettes as a cessation treatment for patients with cancer. Cancer 2014;120:3527–3535. © 2014 American Cancer Society.