A COMPREHENSIVE review of the scientific litera ture on adolescent smoking published in English since 1970 shows a remarkable worldwide pattern of development in adolescent smoking. One developed country after another has reported figures showing that girls now have a higher prevalence than boys. No single factor known to be associated with the uptake of smoking in this age range would have had a large enough effect or changed enough to account for this phenomenon. Advertising and the introduction of low-tar cigarettes may have partly contributed to this development, but a new hypothesis is proposed. The fact that girls mature earlier has combined with a steady change in social attitudes, helped by the commercial pressures, so that girls now exhibit smoking behaviour similar to boys one or more years older. Advertising aimed at young women must be discouraged, and anti-smoking education pro grammes in schools should be revised with particu lar reference to their relevance for adolescent girls.