BACKGROUND: We aimed to examine whether the timing of adiposity rebound (AR) could be a predictive index of body size in Japanese adolescents. METHODS: The longitudinal individual data of 1438 Japanese children, including 714 boys and 724 girls born between 2001 and 2007, were obtained from child health check-ups conducted at ages 1.5, 2, 3, and 5 years, and then yearly after the age of 6 years. We examined whether the timing of AR could be used to estimate the body size at 14 years of age. RESULTS: The AR had a normal distribution with a mean occurrence at age 6-7 years. The odds ratio of having obesity at age 14 were 8.32 for boys and 4.81 for girls, whereas boys and girls with later AR at the same age had a relative risk of thinness of 6.27 and 8.14, respectively. The probability that children with an early AR (i.e., <6 years old) would be obese was nearly 40%. Similar to obesity, the probability of thinness at 14 years remained approximately 8% for both sexes. CONCLUSIONS: The findings suggest that early AR could raise the risk of obesity, and AR could later raise the risk of thinness. However, both probabilities of AR timing as predictors of adolescent weight status may only be about 10%-20%. This study cannot clearly determine whether the results were influenced by other factors after controlling for the timing of AR. Future studies that also consider lifestyle and genetic factors are warranted.