Electronic cigarettes (e-cigarettes) are vaporisers of liquids often containing nicotine. In the inhaled aerosol carcinogens, ultrafine and metal particles are detected usually in concentrations below those measured in tobacco smoke. Therefore, these products are expected to be less harmful. This has not yet been proven. The long-term safety of e-cigarettes is unknown. Short duration use leads to airway irritation and increased diastolic blood pressure. So far only two randomised controlled trials have investigated efficacy and safety of e-cigarettes for smoking cessation: No clear advantage was shown in comparison to smoking cessation medication. Due to insufficient evidence, e-cigarettes cannot be recommended for smoking cessation. Problematic are the lack of regulation and standardisation of e-cigarette products, which makes general conclusions impossible.