BACKGROUND: Training residents in smoking cessation counseling could be part of tobacco control policy. The effect of such an intervention is unknown in Europe. This study provides an assessment of smoking cessation counseling practices by Swiss residents after an intervention based on behavioral modification. METHOD: In a pre-post blind test trial on smoking cessation counseling practices, residents' perceptions about their own ability to counsel smoking behavior among smoking patients were evaluated for 15 residents trained in general internal medicine and in 247 and 155 smoking patients' reports, respectively before and after a training intervention targeting residents, based on behavioral theory of smoking cessation. RESULTS: Changes in counseling were assessed by interviews with patients. After the intervention, residents asked about smoking habits (77 vs 68%), advised to quit (43 vs 28%), provided counseling for cessation (25 vs 10%), gave self-help materials (7 vs 1%), and arranged follow-up visits (5 vs 1%) more often than before. Residents' self-perception of confidence (5.4 vs 4.6/10) and effectiveness (5.3 vs 4.0/10) in counseling also increased after the intervention. After adjusting for daily cigarette consumption and smoking duration, the likelihood of attempting to quit smoking at either 6 or 12 months was increased in the group of patients attended after the intervention (odds ratio 1.52, 95% confidence intervals 1.07-2.48). However, the likelihood of quitting smoking was not increased among these patients (odds ratio 1.07, 95% CI 0.96-1.14). CONCLUSIONS: Short-term smoking cessation counseling by residents was substantially improved by the intervention. Smokers attended after the intervention were more likely to attempt to quit smoking, but not to have quit at 6- or 12-month follow-up.