AIM To investigate effects of cigarette consumption level and socio-economic circumstances during adolescence on adult smoking. METHODS 1958 British birth cohort (all births 3–9 March 1958). Logistic regression used to predict (i) smoking at 41 years and (ii) persistent smoking (at 23, 33 and 41 years) from cigarette consumption and socio-economic circumstances at 16 years, indicated by social class and educational qualifications. RESULTS Of 6537 subjects with full smoking history, 30% smoked at 16 years, 23% smoked at 41 years and 19% smoked at 23, 33 and 41 years (persistent smokers). Heavier smokers at 16, 23 and 33 years were more likely to smoke at 41 years than lighter smokers. The odds ratio (OR) of smoking at 41 years was 2.5 for men and 3.0 for women who smoked ≥60 cigarettes/week at age 16, relative to