Purpose: To evaluate the awareness of cigarette smoking as a risk factor for chronic periodontitis in patients either undergoing active periodontal treatment (APT) or enrolled in supportive periodontal therapy (SPT). Materials and Methods: Comprehensive tobacco use history was collected with a questionnaire in 50 patients before and after APT (test) and in 50 patients (control) enrolled in SPT at the School of Dental Medicine, University of Bern. Carbon monoxide (CO) exhalation levels were measured in both APT and SPT patients. Results: In the test group, 94% (n = 47) completed the study. Before APT, 48% of these (n = 24) knew about the association between smoking and periodontal disease, while 42% (n = 21) assumed a possible association and 10% (n = 5) did not. Following APT, 53% (n = 25) knew about the association, while 34% (n = 17) still assumed a possible association and 10% (n = 5) did not. In the control group, 60% (n = 30) of SPT patients knew about the association of smoking with periodontal disease, while 30% (n = 15) assumed an association and 10% (n = 5) were not aware of any association. In both APT and SPT patients, neither between-group nor baseline to follow-up differences were detected (p > 0.05). Conclusions: Brief interventions for tobacco cessation during APT or SPT failed to increase periodontal patients' awareness of smoking as a risk factor for chronic periodontitis. In order to both increase awareness and motivation to quit tobacco use, more counseling than conventional brief interventions may be needed. Key words: chronic periodontitis, exhaled carbon monoxide, patient education, risk factor, smoking, smoking cessation Keywords: chronic periodontitis, exhaled carbon monoxide, patient education, risk factor, smoking, smoking cessation