The growth, development, and maintenance of bone are influenced by genetic and environmental variables. Understanding variability in bone microstructure among primates may help illuminate the factors influencing the number and size of secondary osteons. The purpose of this study is to assess the bone microstructure in 8 humeral and 12 femoral sections of 12 juvenile chimpanzees, aged 2–15.3 years, and one adult chimp. Secondary osteons were counted and measured for 16 fields per section. Results indicate that the femur exhibits a mean osteon population density (OPD) of 4.46 ± 2.34/mm2, mean Haversian canal area of 0.0016 ± 0.0007 mm2, and mean osteon area of 0.033 ± 0.006 mm2. The humerus has a mean OPD of 4.72 ± 1.57/mm2, mean Haversian canal area of 0.0013 ± 0.0003 mm2, and mean osteon area of 0.033 ± 0.005 mm2. Differences are not significant between the humerus and femur, possibly indicating similar mechanical demands during locomotion. Osteon population density exhibits a moderate correlation with age (r = 0.498) in the femur of the juvenile chimps, but the adult chimp has an OPD of 10.28/mm2, suggesting that osteons likely accumulate with age. Females exhibit higher osteon densities in the periosteal envelope compared to males in the humerus, indicating more remodeling during periosteal expansion. Overall similarities between chimpanzees and humans as well as previously published data on Late Pleistocene hominids (Abbott et al.: Am J Phys Anthropol 99 1996 585–601) suggest that bone microstructure has been stable throughout human evolution. Am J Phys Anthropol, 2009. © 2009 Wiley-Liss, Inc.