As shown in more than 16 000 white participants in two major studies, menarcheal timing is a major determinant of weight and fatness in early adulthood. Early-maturing women are slightly shorter than late-maturing women but weigh 4 kg more. Early maturers are 30% fatter than late maturers, approximately +0.46 Z scores for each of four different skinfolds. Early maturers are far more often obese than late maturers (risk ratio = 1.8). The data suggest that maturational timing has a greater long-term effect on the level of fatness than the level of fatness had on maturational timing.