Introduction: Although bacterial plaque is regarded as the major cause of periodontitis, the role of smoking as an important risk factor has been established in the progression of periodontal disease. Thus, the present study aimed to evaluate knowledge and attitude of patients with periodontitis concerning effects of smoking on periodontal health.

Method: In this descriptive cross-sectional study, 300 patients with periodontitis, aged between 18-74 years, were selected via convenience sampling out of patients referred to Periodontology Department of Shahid Sadoughi Dental Faculty and Khatam Alanbia professional clinic of Yazd. The study data were collected using a questionnaire, which were then analyzed by SPSS software (ver. 17) applying Chi-square, T-test and ANOVA statistical tests.

Results: The mean total scores of patients' knowledge and attitude in regard with smoking effect on periodontal health were reported 86.7±18.4 and 48.1±7.3, respectively. A significant relationship was observed between knowledge and attitude with students' educational level. In the present study, 42% of smokers tried to quit smoking at least once, among which 14.3% of cases occured due to oral and dental health as well as consultation with dentists.

Conclusion: The study findings showed despite patients' good knowledge concerning the effect of smoking on periodontal health, their attitude was reported moderate. Patients' moderate attitude can be mentioned as the main reason of continuing smoking despite their good knowledge. Moreover, dentists were demonstrated to have a negligible role with respect to patients' awareness in this regard.