Objective: To test the hypothesis that adolescent body mass index (BMI) tracks into adulthood and can be used as a predictor of obesity and/or central adiposity in adulthood. Method: A prospective cohort study following up 111 female and 84 male subjects who participated in dietary and anthropometric surveys when aged 12 years (in 1979-1981) and 33 years (in 2000-2001). At both time points, height and weight were measured and BMI calculated. At 33 years, waist circumference (WC) and hip circumference were also measured and waist-to-hip ratio (WHR) calculated. Results: In the male and female participants, BMI at 12 years was associated significantly with BMI at 33 years (R = 0.58 and 0.53, respectively, both p < 0.01) and WC at 33 years (R = 0.58 and 0.53, both p < 0.01). The probability of being an obese adult increased with rising adolescent BMI: normal weight male (BMI < 20.89 kg/m 2) and female subjects (BMI < 21.20 kg/m 2) at 12 years had a 20% and a 7% chance of being obese at 33 years, respectively; the probabilities for obese male (BMI ≥25.58kg/m 2) and female subjects (BMI ≥26.05kg/m 2) were 83 and 64%. The corresponding probability of becoming centrally obese (measured by WC) increased from 17 and 16% in male and female subjects of a normal weight to 58 and 59% in those being obese. Conclusions: Adolescent BMI is a good predictor of adult BMI and WC and the likelihood of becoming obese and/or centrally obese in adulthood.