United States has experienced a widespread obesity epidemic. However, it is unclear whether the obesogenic environment has uncovered genes previously unimportant in adiposity or whether genes influencing obesity are the same before and after the obesity epidemic. The objective of this study was to test whether BMI pre- and postobesity epidemic would be controlled by shared genetic effects. A 25-30-year follow-up of parents and children who participated in the National Institutes of Health-National Heart, Lung, and Blood Institute Lipid Research Clinics (LRC) Princeton School Study, 1973-1976, were followed up in 1999-2004 in the Princeton Follow-up Study (PFS). Heritability of BMI and genetic correlations between pre-epidemic BMI and BMI z-scores in adolescents and postobesity epidemic BMI were calculated. Even though they had similar ages, offspring had higher BMI in PFS than their parents in LRC (28.5 +/- 6.6 vs. 26.1 +/- 4.4, P < 0.0001). BMI measurements in offspring were strongly heritable (BMI(LRC): h(2) = 0.78 +/- 0.17; BMI z-score(LRC): h(2) = 0.61 +/- 0.16; BMI(PFS): h(2) = 0.64 +/- 0.16, all P < or = 0.0001). Further, the change of BMI exhibited a high heritability (h(2) = 0.51 +/- 0.18, P = 0.003). Bivariate analysis of BMI in LRC and PFS showed significant genetic correlation (0.70 +/- 0.16, P = 0.005), whereas the environmental correlation was not significant (0.36 +/- 0.17). Although the obesogenic environment may have changed between the 1970s and 2000s, many of the same genes are likely to be involved in establishing genetic susceptibility to obesity. Furthermore, shared genetic effects survive the period of the transition from adolescence to adulthood.