Background: The BMI distribution shifted upward in the United States between the 1960s and the 1990s, but little is known about secular trends in the pattern of BMI growth, particularly earlier in the century and early in childhood. Objective: The objective was to examine differences in BMI growth in children born in 1929-1999. Design: BMI curves from ages 2 to 18 y were produced for 855 European-American children in the Fels Longitudinal Study born in 1929-1953, 1954-1972, and 1973-1999. Age (Amin) and BMI (BMI min) at adiposity rebound and age (AVmax), BMI (BMIV max), and velocity (Vmax) at maximum velocity were derived; multivariable regression was used to examine whether maternal BMI, infant weight gain, and other covariates mediated the cohort effects on these traits. Results: BMI curves showed that children born in 1973-1999 had the lowest BMI values until age 5 y but had the largest values from age 8 y onward. In adjusted models, boys and girls born in 1973-1999 had a 0.15-kg/m2 per year faster Vmax and a 1-kg/m2 higher BMIV max than did children of the same sex born in 1929-1953, and girls had a 0.8-y earlier Amin (P < 0.01). Maternal BMI and infant weight gain were associated with an obesity-prone pattern of BMI growth but did not account for the observed trends. Conclusions: Shifts in the BMI growth rate around the time of pubertal initiation were apparent starting after 1973. The BMI growth curve did not increase monotonically over time; rather, children born during the obesity epidemic were characterized by lower BMI values before the adiposity rebound and by rapid subsequent BMI gain.