It is broadly believed that smokers who have ceased to smoke before the age of 30 years, have no excess health risk compared with never-smokers. As summarised in this review, large, prospective cohort studies show, that this holds true regarding all-cause mortality for men, whereas the risk of dying remains slightly elevated for women, who quit smoking early. The risk of lung cancer also remains elevated. Smoking also increases the risk of physical and mental problems in youth. The evidence is strongest regarding infertility, impotence, reproductive health outcomes, cardio-vascular and respiratory symptoms.