BACKGROUND: Reviews state that there is a room for improvements of smoking cessation (SC) intervention in general practice. METHODS: In 2005, all 61 general practitioners (GPs) in four municipalities in Copenhagen, Denmark, were invited to participate. Twenty-four GPs accepted and were cluster randomized to one of three groups: Group A, referral to group-based SC counselling (national model), n = 10; Group B, referral to internet-based SC programme (newly developed), n = 8; or Group C, no referral ('do as usual'), n = 6. A total of 1518/1914 smokers were included, and 760 returned a questionnaire at 1-year follow-up. RESULTS: The participating GPs reported significantly more SC counselling than GPs who refused participation (P = 0.04). Self-reported point abstinence was 6.7% (40/600), 5.9% (28/476) and 5.7% (25/442) in Groups A, B and C, respectively. Only 40 smokers attended group-based SC counselling, and 75 logged in at the internet-based SC programme. In cluster analyses, we found no significant additional effect of referral to group-based (OR: 1.05; 95% CI: 0.6-1.8) or internet-based SC programmes (OR: 0.91; 95% CI: 0.6-1.4). CONCLUSIONS: We found no additional effect on cessation rates of GPs' referring to group-based SC counselling or internet-based SC programme. This finding might, to some degree, be explained by the short time used by the GPs on SC counselling and the selection of the participating doctors.