Evidence from cross-sectional and case-control studies in various populations demonstrates that adult smokers are approximately three times as likely as non-smokers to have periodontitis. The association between smoking and attachment loss is even stronger when the definition of periodontitis is restricted to the most severely affected subjects. Smokers have a diminished response to periodontal therapy and show approximately half as much improvement in probing depths and clinical attachment levels following non-surgical and various surgical modalities of therapy. Implant failures in smokers are twice those of non-smokers, with a higher failure rate in the maxillary arch accounting for the majority of the difference. Tobacco-induced alterations in microbial and host factors contribute to these deleterious effects of smoking on the periodontium. In longitudinal studies, the rate of periodontal disease progression is increased in smokers, but decreases to that of a non-smoker following tobacco cessation. Likewise, recent non-smokers respond to periodontal therapy in a manner similar to patients who have never smoked. Data regarding the impact of smoking on periodontal status included in this review will be helpful to dental health professionals as they counsel their patients regarding tobacco use. The role of dental health professionals in tobacco cessation is discussed, including the use of the five A's: ask--identify tobacco users; advise--advise them to quit; assess--evaluate the patient's readiness to quit; assist--offer assistance in cessation; and arrange--follow up on the patient's cessation efforts. The addition of pharmacotherapy to behavioral therapy, including nicotine replacement therapy and bupropion, can increase cessation rates. The most popular form of nicotine replacement therapy is the patch, and its use has been shown to double cessation rates compared to behavioral therapy alone. Use of bupropion in combination with nicotine replacement therapy may be particularly helpful for heavy smokers or smokers who have experienced multiple failed attempts at cessation. The American Academy of Periodontology Parameters of Care include tobacco cessation as a part of periodontal therapy, and the 2000 Surgeon General's Report on Oral Health in America encourages dental professionals to become more active in tobacco cessation counseling. Doing so will have far-reaching positive effects on our patients' oral and general health.