Introduction: Little is known about the pattern of electronic cigarette (e-cigarette) use over time or among smokers with medical comorbidity. Methods: We assessed current cigarette smokers' use of e-cigarettes during the 30 days before admission to 9 hospitals in 5 geographically dispersed US cities: Birmingham, AL; Boston, MA; Kansas City, KS; New York, NY; and Portland, OR. Each hospital was conducting a randomized controlled trial as part of the NIH-sponsored Consortium of Hospitals Advancing Research on Tobacco (CHART). We conducted a pooled analysis using multiple logistic regression to examine changes in e-cigarette use over time and to identify correlates of e-cigarette use. Results: Among 4,660 smokers hospitalized between July 2010 and December 2013 (mean age 57 years, 57% male, 71% white, 56% some college, average 14 cigarettes/day), 14% reported using an e-cigarette during the 30 days before admission. The prevalence of e-cigarette use increased from 1.1% in 2010 to 10.3% in 2011, 10.2% in 2012, and 18.4% in 2013; the increase was statistically significant (p < .0001) after adjustment for age, sex, education, and CHART study. Younger, better educated, and heavier smokers were more likely to use e-cigarettes. Smokers who were Hispanic, non-Hispanic black, and who had Medicaid or no insurance were less likely to use e-cigarettes. E-cigarette use also varied by CHART project and by geographic region. Conclusions: E-cigarette use increased substantially from 2010 to 2013 among a large sample of hospitalized adult cigarette smokers. E-cigarette use was more common among heavier smokers and among those who were younger, white, and who had higher socioeconomic status.