Dental professionals are in a unique position to promote smoking cessation among their patients. We evaluated the effects of a brief counselling intervention by a dentist on patients’ attitude towards the role of dentists in tobacco cessation programmes. In a semi-experimental study in Tehran, Islamic Republic of Iran, 70 eligible smokers were selected and randomly assigned to intervention and control groups. The initial attitudes of the patients regarding tobacco cessation counselling services provided by the dentist were determined using a validated questionnaire. The intervention group received a brief chair-side counselling by a dentist based on the 5 A’s approach, while no intervention was provided for the control group. At 8-weeks follow-up, smokers receiving the intervention showed significantly more positive attitudes towards the role of the dentist in advising patients to quit smoking compared with those in the control group. More responsibility could be transferred to dentists for tobacco prevention.