Promotion of optimal growth while preventing the emergence of obesity in childhood requires an understanding of the dynamics over time of linear growth and weight for height. To assess long-term secular trends in height-for-age and BMI for age in children <6 y old, we analyzed a series of cross-sectional surveys conducted between 1968 and 2007 in 4 villages in eastern Guatemala. We used height and weight of children <6 y old (n = 507, 606, 627, 704, 526, and 502 for survey years 1968, 1972, 1977, 1988, 1997, and 2005-7, respectively) to compute height-for-age Z-score (HAZ) and BMI-for-age Z-score (BMIZ) based on WHO growth standards. HAZ was -2.73 +/- 1.12 (mean +/- SD) in 1968 and -1.16 +/- 1.16 in 2005-7 (P < 0.001). The prevalence of stunting (HAZ <-2.0) was 73.0% in 1968 and 23.1% in 2005-7 (P < 0.001). Among children 57-63 mo old, HAZ in 2005-7 was 1.20 (95% CI, 0.79, 1.62) SD units higher than in 1968, corresponding to 5.6 cm in boys and 5.7 cm in girls. For all survey years except 2007, BMIZ increased through age 36 mo, then declined; for the 2005-7 sample, BMIZ did not vary by age. The prevalence of BMIZ >1.00 was 21.1% in 1968 and 19.6% in 2005-7 (P > 0.05); for BMI <-1.00, the respective prevalences were 7.9% and 5.2% (P > 0.05). There have been long-term improvements in child growth, as measured by HAZ, without concurrent increases in BMI over successive generations of children.