This study examined weight status during adolescence and young adulthood, and young adult health condition diagnosis. Data are from 10,439 African-American, Hispanic, and white men and women participating in the National Longitudinal Study of Adolescent Health during Waves 1 (adolescence: ages 12–19) and 3 (young adulthood: ages 19–26). Categories were created differentiating individuals based on their weight status during adolescence and young adulthood: (i) obese during adolescence and young adulthood (i.e., continuously obese), (ii) obese during adolescence only, (iii) obese during young adulthood only, and (iv) never obese. Multilevel random intercept regression models were used to examine the impact of obesity category, sex, and race/ethnicity on young adult asthma, diabetes, high cholesterol, and high blood pressure. Continuous obesity increased the likelihood for young adult disease and health risk conditions compared to individuals who were never obese. Obesity isolated to adolescence (Wave 1) increased the likelihood for high cholesterol and high blood pressure, whereas obesity isolated to young adulthood (Wave 3) also increased the likelihood for diabetes—all increases were relative to nonobese weight status during both periods. Associations varied in direction and degree when sex and race/ethnicity were considered. Findings clarify some of the mixed understandings regarding the associations between age of onset and stability of obesity, and health outcomes with important public health implications. Although results indicate obesity isolated to a single developmental period does have health repercussions, obesity experienced continuously during adolescence and young adulthood greatly intensified risk across all health conditions.