This study examines the evolution of size differences among papionin primates by measuring hormones that regulate size growth during ontogeny and influence ultimate adult size (insulin-like growth factor-I (IGF-I), insulin-like growth factor binding protein-3 (IGFBP-3), growth hormone binding protein (GHBP), dehydroepiandrosterone sulfate (DHEAS), testosterone, estradiol). The analyses assess longstanding ideas about circulating hormone levels and body size. Importantly, because the consensus papionin molecular phylogeny implies at least two episodes of size increase, this study offers opportunities to determine whether or not similar hormone profiles regulate this apparent evolutionary convergence (i.e., do larger-bodied papionins have higher levels of growth-related hormones than smaller-bodied papionins?). Five hundred and sixty serum samples (from 161 individuals) from 11 papionin species were analyzed using a two-level approach to address this issue. One used mixed longitudinal samples from two papionin species to test whether, during growth, large- and small-bodied species have higher and lower hormone levels, respectively. The second compared multiple papionin species to assess whether or not hormone levels covary with size in adult animals. Result show that size and hormone levels do not covary consistently across papionins, either during growth or in adulthood. Specifically, some smaller-bodied papionin species have higher absolute hormone levels than larger-bodied species. Differences in some hormone levels appear to track phylogeny more closely than body size. In contrast to studies based on single species, we demonstrate that, while the hormones analyzed affect growth, absolute circulating hormone levels either during growth or adulthood may be decoupled from interspecific differences in body size. Am J Phys Anthropol, 2007. © 2006 Wiley-Liss, Inc.