Introduction: Electronic cigarette (e-cigarette) use has grown significantly in some European Union (EU) Member States (MS). A better understanding of the exposure to secondhand e-cigarette aerosols (SHA) is necessary to develop and implement comprehensive regulations on e-cigarette use in public places. This study aims to assess the observation of e-cigarette use in public places, the self-reported exposure to SHA, and the level of users' comfort using e-cigarettes in the presence of others. Methods: This is a cross-sectional study of the Wave 1 International Tobacco Control 6 European Countries Survey recruiting adult smokers (n=6011) across six EU MS: Germany, Greece, Hungary, Poland, Romania, and Spain, within the EURESTPLUS Project. A descriptive analysis was conducted to estimate the prevalence (%) of observed e-cigarette use in different places, frequency of self-reported exposure to SHA, and level of comfort using e-cigarettes in the presence of others. Results: In all, 31.0% of smokers observed others using e-cigarette in public places, 19.7% in indoor places where smoking is banned, and 14.5% indoors at work. Almost 37% of smokers reported to be ever exposed to SHA, ranging from 17.7% in Spain to 63.3% in Greece. The higher prevalence of observed e-cigarette use and passive exposure to SHA was reported by smokers of younger age, of higher educational level and those being current or former e-cigarette users. Part (8.8%) of the smokers who were also e-cigarette users reported feeling uncomfortable using e-cigarettes in the presence of others. Conclusions: A third of smokers from six EU MS reported being exposed to SHA. Prevalence differences were observed among the countries. In the context of scarce evidence on long-term health effects of exposure to SHA, precautionary regulations protecting bystanders from involuntary exposure should be developed.