- Objective. Identification of children at risk for adolescent overweight can assist in targeting interventions. Uncertainty remains regarding the validity of current body mass index (BMI) reference values in predicting future risk on a population basis. This study aimed to assess the validity of current childhood adiposity classifications in predicting adolescent overweight and obesity among Israeli youth. Design. Historical cohort study. Setting. School-based childhood health studies and adolescent physical examinations. Participants. A total of 3 163 subjects surveyed first at age 8–15 and again at age 17–19. Observations. Age, sex, height, weight and BMI. Outcome measures. Sensitivity, specificity, positive and negative predictive values, and relative risk of childhood adiposity classification. Results. Childhood overweight and obesity showed low sensitivity and high specificity for predicting adolescent overweight and obesity. Positive predictive values were low and varied by age and sex, but negative predictive values were consistently high in both sexes and all ages (range 0.85–0.99). After adjusting for age and sex, both childhood overweight and obesity substantially increased the risk of adolescent overweight (relative risk [RR] 7.03 and 7.20, respectively) and adolescent obesity (RR 24.34 and 28.41, respectively). Conclusions. Childhood overweight and obesity are strong risk factors for adolescent overweight and obesity among Israeli youth. Normal weight children were at very low risk for adolescent overweight. These findings suggest that population-based health promotion aimed at maintaining normal weight among children should be given preference over risk-guided approaches targeting weight reduction among obese children.