OBJECTIVE: To test the feasibility and efficacy of an internet program for smoking cessation during and after inpatient treatment in rehabilitation centers. METHODS: A total of 7574 consecutively admitted inpatients from three German rehabilitation centers were assessed for smoking status. Daily smokers or former daily smokers who regularly used the internet and e-mail were proactively invited for study participation. Out of 749 eligible patients, 477 (64%) participated in the study and were randomly assigned to an intervention or an assessment only control group based on the calendar week of admission. Patients of the intervention group had the possibility to use an internet program for smoking cessation for a period of six months. The program provided at least one but up to seven individual counseling sessions through a computer expert system, informational websites and a message board. RESULTS: At six-months follow-up, seven-day point prevalence smoking abstinence was twice as high in the intervention group as in the control group (OR=2.0; CI 1.1-3.8; p=.02). CONCLUSIONS: Proactive recruitment of smokers in combination with the provision of an internet program for smoking cessation allow for an inexpensive and effective smoking cessation support during and after inpatient rehabilitation treatment.