Although smoking is one of the major risk factors for the development of atherosclerosis, the exact mechanism of smoking-related vascular disease is not known. Smoking causes acute hemodynamic alterations such as increase in heart rate, systemic and coronary vascular resistance, myocardial contractility, and myocardial oxygen demand. These short-term effects could lower the ischemic threshold in smokers with coronary artery disease and contribute to the increased risk for acute cardiovascular events. Endothelial damage is thought to be an initiating event in atherosclerosis and early studies have demonstrated that long-term smoking has direct toxic effects with structural changes of human endothelial cells. Recent research has shown the importance of the functional role of the endothelium in regulating normal vascular tone, platelet-endothelial interactions, leukocyte adhesion and smooth muscle cell proliferation via synthesis and release of a variety of substances such as nitric oxide. There is strong evidence that smoking leads to endothelial dysfunction in both conductance and resistance vessels. This effect seems to be dose-related and reversible. The mechanism of endothelial dysfunction in smokers is not known, but increased degradation of nitric oxide by oxygen-derived free radicals has been suggested. In addition, smoking could cause oxidative inactivation of tetrahydrobiopterin, a critical cofactor of nitric oxide, leading to an uncoupling of the endothelial nitric oxide synthase with increased superoxide production and decreased nitric oxide bioactivity. Other pro-atherosclerotic effects of smoking are discussed. Given the enormous health hazard of tobacco use, complete abstinence from smoking should be achieved. Smoking cessation counseling should be given to healthy subjects and even more vigorously to patients with manifested disease. Every effort should be undertaken to prevent children and adolescents from starting to smoke. Brief tobacco dependence treatment is effective, and every tobacco user should be offered at least brief treatment at every office visit. More intensive treatment is more effective in producing long-term abstinence from tobacco. Nicotine replacement therapy (nicotine patches or gum), clinician-delivered social support, and skills training are the three most effective components of smoking cessation treatment.