Introduction: The use of e-cigarettes has spread very rapidly. However, there is little data available regarding their safety, their effectiveness in helping people quit smoking, or their potential to facilitate a transition to tobacco use. Preliminary data from the Constances cohort describe the prevalence of tobacco and e-cigarette use and trends over a one-year period. Materials and Methods: A cross-sectional analysis (n=24,157) describes e-cigarette and tobacco use according to sociodemographic characteristics, perceived health status, and depression. Consumption trajectories over one year (n=8,042) are also presented. Results: E-cigarette use among non-smokers is very rare (11 subjects) and slightly more common among former smokers (1%); combined use of cigarettes and e-cigarettes is twice as common. Prevalence rates are similar across both genders and decrease with age among dual users and former smokers. The frequency of mixed use appears to be higher among office workers and manual laborers. Mixed users have the lowest proportion of individuals who rate their health as Very Good/Good and the highest frequency of depressive symptoms. There is a gradient in e-cigarette frequency based on pack-years of tobacco use. The one-year follow-up shows that no exclusive e-cigarette users became smokers one year later. Discussion: These preliminary results do not suggest that e-cigarettes facilitate the transition to tobacco and suggest that they are instead widely used to quit smoking; a long-term follow-up in Constances is planned.