Tobacco is the single most important cause of avoidable morbidity and early mortality in many countries. Smoking cessation is associated with a reduction in the prevalence of related symptoms as well as a progressive decrease in the occurrence of related diseases. Thus, there is a rapid decline in the occurrence of cardiovascular diseases in individuals who stop smoking; there is also a decline in the occurrence of lung cancer, although delayed and with a slower decrease rate. This is an important message for physicians and patients: Physicians should systematically offer counselling and information to their patients who smoke. The message should be tailored to the patient's status and must be different for a patient who has already decided to quit than for a patient who is not considering cessation in the near future. To help patients who have decided to stop and incite other patients who smoke to quit, physicians should be aware of the mechanisms involved in acquiring and breaking tobacco dependence (learning pathways, physiological dependence, behavioral analysis). Physicians should be trained to use methods which have proved effective in a physician's practice and to manage difficulties which may arise during cessation (e.g. craving, weight gain), as well as appropriate use of nicotine skin patches or chewing gum. From a public health standpoint, widespread action by physicians to promote smoking cessation among their patients could be one of the most effective clinical preventive measures.