Little research, particularly involving longitudinal prospective cohort studies, has investigated factors in earlier life that influence later adult patterns or frequency of smoking, including factors which lead individuals not only to initiate smoking early, but also to quit in late adolescence before developing physical or psychological dependence. We examined childhood and adolescent predictors of the patterns and frequency of smoking at 21 years. Participants consisted of a subgroup of 3522 youth (52% female) from the Mater-University of Queensland Study of Pregnancy, for whom social, family and individual factors in childhood (5 years) and adolescence (14 years), as well as smoking status at 21 years, were measured. Unadjusted odds ratios and 95% confidence intervals were estimated using multinomial logistic regression, and multivariable associations were evaluated using progressive multinomial logistic regression models. Results showed that marital changes between 5 and 14 years, paternal smoking at 14 years, and adolescent alcohol use and externalizing behaviours were independently associated with 'smoking regularly' and 'used to smoke' patterns. Above-average adolescent school performance was protective for both groups, with higher maternal level of education being protective for the 'smoke regularly' group. Maternal smoking at 14 rather than 5 years was a risk factor for 'regular smokers', while maternal smoking at 5 but not at 14 was protective and associated with the 'used to smoke' pattern. The findings highlight the protective factors of mothers' quitting between 5 and 14 and youth being more likely to quit, and markers of developmental risk, as well as protective factors, particularly in adolescence, that may be targeted in efforts to influence the pathway to adult smoking. The findings imply that public health policy and smoking cessation interventions should focus more attention on families from disadvantaged socioeconomic backgrounds and specifically tailored to their needs.