The need to focus on the prevention of obesity and excessive weight gain in young adults is convincingly illustrated in the study by Zheng and colleagues1 in this issue of JAMA. Using data from 92 837 women in the Nurses’ Health Study (NHS) and 25 303 men in the Health Professionals Follow-Up Study (HPFS) who recalled weight at young adulthood (at age of 18 years in women and age of 21 years in men) and reported current weight at middle adulthood (age of 55 years), the authors found that approximately 23% of women and 13% of men gained 20 kg or more between the ages of 18 and 55 years in women and between the ages of 21 and 55 years in men. In both groups, the incidence of type 2 diabetes, hypertension, cardiovascular disease, cataracts, severe osteoarthritis, and mortality was increased with weight gain in a dose-response fashion, and was greatest among those who gained 20 kg or more. Obesity-related cancers in both women and men were associated with moderate weight gain during adulthood.