Patterns of tibia long bone growth were examined for the Libben Late Woodland and Bt-5 Late Archaic hunter-gatherer skeletal groups. Subadults included in the analyses ranged in age from birth to 10 years. The primary goals were to (1) identify potential differences in relative tibia growth and (2) evaluate the extent to which such differences were concordant with demographic and epidemiological characteristics of the two groups. Methods used were designed to minimize the shortcomings of unknown age and sex of the skeleton, small sample sizes, and population differences in adult size attained. Results showed that Bt-5 preadolescent growth performance and health status in general were superior to those of the Libben group. Modifications in the rate and timing of Libben tibia growth occurred early and were primarily restricted to the weaning period. It is suggested that high levels of infectious disease experienced in the first years of life at Libben played a substantial role in the etiology of (1) early long bone growth retardation, (2) a greater prevalence of iron deficiency anemia in the childhood years, and (3) elevated levels of subadult morbidity and mortality compared to Bt-5. Palaeodemographic, palaeoepidemiological, and modern comparative population data that support these inferences are discussed.