Introduction: the internet offers an interesting alternative to face-to-face and telephone-based support for smoking cessation. This study was designed to assess the effectiveness of a personalized and automated internet-based program. Methods: French current adult smokers willing to quit within 2 weeks were recruited for a randomized controlled trial. The intervention consisted of an automated program of 45 e-mails ("e-coaching") sent over a 3-month period. The control group received a PDF version of a booklet on smoking cessation. Self-reported 7-day point prevalence smoking abstinence was measured at 6 months (primary outcome), at 3 and 12 months of follow-up (secondary outcomes). Results: 2,478 smokers were randomized (1,242 for e-coaching, 1,236 for the booklet). Cessation rate in the intention-to-treat population was not significantly different between the two groups at 6 and 12 months, but was higher in the e-coaching group at 3 months than in the control group (27.5% vs 23.5%, p=0.02, OR=1.24, CI=[1.03-1.49]). After adjustment for baseline conditions, the effect of the intervention in the per-protocol (PP) sample was significant at 3 months (aOR=1.72 [1.31-2.28], p<0.001, N=1042) and at 6 months (aOR=1.27 [1.00-1.60], p=0.05, N=1082). GLM repeated measure analyses showed significant group by time interaction in the ITT and a significant group effect in the PP population. Conclusions: analyzed intention-to-treat, e-coaching was superior to a booklet at 3 months (end of intervention) but no more superior at 6 and 12 months follow up. Among those who actually followed the program, the effectiveness is also observed 3 months after the intervention is stopped.