Cigarette smoking has long been suspected to be associated with a variety of oral conditions including periodontal diseases. Experimental evidence accumulated over the last 2 decades has indicated that cigarette smoking is probably a true risk factor for periodontitis. This environmental exposure has been associated with 2- to 3-fold increases in the odds of developing clinically detectable periodontitis. Smokers have both increased prevalence and more severe extent of periodontal disease, as well as higher prevalence of tooth loss and edentulism, compared to non-smokers. The greater severity of periodontal destruction may be partly accounted for by the reported increases in the rate of periodontal disease progression. The noxious effect of smoking has been shown to be dose dependent and to be particularly marked in younger individuals; in these subjects, up to 51% of the observed risk of periodontitis was associated with smoking. Much of the literature has also indicated that smokers affected with periodontitis respond less favorably to both non-surgical, surgical, and regenerative periodontal treatments. The success rate of dental implants has also been shown to be compromised in smokers. Furthermore, longterm studies have pointed out that smoking was associated with recurrence of periodontitis during periodontal maintenance; the effect appeared to be dose dependent, with heavy smokers (> 10 cigarettes/day) presenting with higher levels of disease progression. The indication that previous smokers have lower levels of risk for periodontitis compared to current smokers is considered to be the strongest available evidence that smoking cessation will result in improved periodontal health and that smoking cessation counseling should be an integral part of periodontal therapy and prevention. So far, however, no randomized controlled clinical trial establishing the effect of smoking cessation and/or reduction on the periodontal outcomes has been reported. Given the present state of uncertainty about the periodontal benefits, but in light of the established general health gains for the patient that could be derived from a smoking cessation program, practitioners are incorporating smoking cessation counseling as an integral part of periodontal therapy. Furthermore, smoking status represents a key parameter to assess the periodontal risk of an individual subject and therefore to make evidence-based clinical decisions.