Objective Obesity is recognized as a significant risk factor for diabetes and hypertension. The present study aimed to examine the associations between adults' obesity risk and childhood and parental obesity. Methods A total of 204 children aged 6-17 years were recruited in 2002 with an average follow-up period of 13.2 years. Height and body weight were measured by trained staffs. Overweight and obesity were defined based on the Chinese standard for children and adults. T-test, analysis of variance, and Chi-square analysis were used for single factor analysis. Multiple linear and logistic regression analyses were used to perform multifactor analysis. Results The percentage of non-obese children who grew up to be non-obese adults was 62.6%, and that of obese children who grew up to be obese adults was 80.0%. There was a significant association between childhood body mass index (BMI) and adulthood BMI with a beta regression coefficient of 3.76 [95% confidence interval (CI): 1.36-6.16], and between childhood obesity and adulthood obesity with an odds ratio of 5.76 (95% CI: 1.37-24.34). There was no statistical difference between parental obesity at baseline and children's adulthood obesity, after adjustment of confounders. Male participants and those aged 10.0-13.0 years had a higher risk of adulthood obesity with odds ratios of 2.50 (95% CI: 1.12-5.26) and 3.62 (95% CI: 1.17-11.24), respectively. Conclusion Childhood obesity is an important predictor of adulthood obesity.