Since 1974 an anti-smoking campaign consisting of a one-day educational intervention has been carried out in primary schools in Milan by the Italian League against Cancer (Milan Division). All but two of the 165 schools were randomized to evaluate the intervention effect. A total of 8549 children aged 9-10 were allocated to the intervention group and 8897 to the control group. Four years later a self-administered questionnaire was distributed in order to investigate the children's smoking habits. The proportion of smokers was 8.05% and 8.72% (p = 0.23) respectively for the intervention and control groups. It was concluded that sporadic educational intervention carried out during primary school years has little or no impact in preventing cigarette smoking in teenagers.