['To test transethnic replication of a genetic risk score for obesity in white and black young adults using a national sample with longitudinal data.', 'A prospective longitudinal study using the National Longitudinal Study of Adolescent Health Sibling Pairs (n\u200a=\u200a1,303). Obesity phenotypes were measured from anthropometric assessments when study members were aged 18-26 and again when they were 24-32. Genetic risk scores were computed based on published genome-wide association study discoveries for obesity. Analyses tested genetic associations with body-mass index (BMI), waist-height ratio, obesity, and change in BMI over time.', 'White and black young adults with higher genetic risk scores had higher BMI and waist-height ratio and were more likely to be obese compared to lower genetic risk age-peers. Sibling analyses revealed that the genetic risk score was predictive of BMI net of risk factors shared by siblings. In white young adults only, higher genetic risk predicted increased risk of becoming obese during the study period. In black young adults, genetic risk scores constructed using loci identified in European and African American samples had similar predictive power.'] Does polygenic risk predict obesity in both white and black young adults?