Cigarette smoking is a risk factor for several diseases, and recent evidence strongly suggests an adverse effect on periodontal health. Nevertheless, the nature of the relationship between smoking and periodontal disease is not clear. Smoking causes defects in neutrophil function, impairs inflammatory and immune responses to periodontal pathogens, and exerts both systemic and local effects. Smoking is associated with an increased rate of periodontal disease in terms of alveolar bone loss and attachment loss, as well as pocket formation. Nicotine, the major component of cigarette smoke, may weaken host defenses to the bacterial invasion induced by plaque.