OBJECTIVE To investigate various aspects of dentists' beliefs and practices with respect to helping their patients stop smoking. DESIGN Postal questionnaire survey conducted in 1996. SETTING The general dental practitioners on the health authority lists of Berkshire, Buckinghamshire, Northamptonshire and Oxfordshire. SUBJECTS The 869 dentists registered on 1 April 1996. RESULTS A high response rate (78%; 674/869) was obtained. The majority of respondents (82%; 95% CI: 79, 85) thought dentists should encourage their patients to stop smoking although only 37% (95% CI: 34, 41) believed dentists to be effective in smoking cessation and even fewer (18%; 95% CI: 15, 21) routinely recorded their patients' smoking status. Of respondents, 51% (95% CI: 46, 55) said they always discussed smoking with patients who had periodontal problems but only 9% (95% CI: 7, 12) always did so with patients who had no major oral health problem. Newer graduates were more likely to routinely record their patients' smoking status (P = 0.02), and to think that doctors' advice (P = 0.001) and nicotine replacement therapy (P < 0.001) were effective in promoting smoking cessation. Dentists in mainly private practices were more active than those in NHS or mixed practices in recording patients' smoking status (P < 0.001) and in discussing smoking (P = 0.002). CONCLUSIONS Most respondents thought that dentists should encourage their patients to stop smoking but few are active in this area.