Cigarette smoking is a risk factor for periodontitis incidence and progression. Contrasting results were obtained when the impact of cigarette smoking on the clinical outcomes of non-surgical periodontal therapy (NSPT) was evaluated. The present study was designed to evaluate the smoking status as outcome determinant of NSPT.Two groups of patients with different smoking status (smoker group, S, and non-smoker group, NS) were retrospectively selected from a pool of patients seeking care for periodontitis. The effectiveness of NSPT was assessed by evaluating the changes in 1) the prevalence of sites with different pocket probing depth (PPD), and 2) the patient- and site-specific bleeding.Group S comprised of 65 patients (mean age: 45.6+/-8.7 years; 24 males and 41 females) and group NS comprised of 66 patients (mean age: 46.8+/-11.7 years; 17 males and 49 females). A statistically significant increase in the prevalence of sites with PPD or =7 mm (P< or =0.01) was detected at re-evaluation. BoP scores were significantly reduced for the entire dentition (P<0.000) as well as for sites with PPD< or =3 mm (P<0.01) and PPD 4/6 mm (P<0.000) in both group S and group NS. No statistically significant differences in the post treatment change of PPD and BoP scores were detected between groups.Our results seem to suggest that smoking status has a limited, if any, effect on the clinical outcomes of NSPT.