Social-living primates experience changes in their physical and social environments throughout their lives. Sometimes-extreme environmental changes lead to fluctuations in food availability and influence the nature of social interactions, changing primates’ energy intake and expenditure on daily and life-long bases. Growth and development before and during puberty creates additional energy demands. Balancing energetic demands of environmental fluctuations and growth with energy available for intake is essential for survival. Using triiodythyronine (T3) concentrations in baboons as a measure of energy balance, this paper seeks to quantify energetic balance from infancy to adolescence, and to analyze which environmental factors best predict T3 concentrations. First, I characterize longitudinal patterns of variation in T3 concentrations both in males and in females. Second, results from model selection show the strong predictive negative effect of sexual maturation and positive effect of cumulative rainfall on T3 concentrations. My results present patterning of T3 concentrations throughout infancy and adolescence and demonstrate how environmental factors and the important transition to adolescence affect the energetic balance necessary for survival. These findings provide a jumping off point for comparison of longitudinal patterning of hormone concentrations during development and open the door for further explorations of energetic balance during puberty.