Food restriction increases life span, reduces aging rate and affects a wide variety of biological functions. In rats, food restriction delays bone growth and reduces bone density and mineral content. We report the effects of aging and long-term (> 6.0 y) food restriction on several indices of bone growth and metabolism in rhesus monkeys (Macaca mulatta). Food allotments for controls approximated free access consumption, whereas food-restricted monkeys received 30% less food on a body weight basis. Cross-sectional and longitudinal age effects on serum alkaline phosphatase paralleled those reported for humans. Food restriction induced a significant delay in the developmental decline (to adult levels) in total alkaline phosphatase and significantly suppressed serum interleukin 6 concentrations, particularly in younger monkeys. Also, food restriction slowed skeletal growth, as reflected by shorter crown-rump length, and significantly reduced total body bone mineral content, but not bone mineral density, measured by dual energy X-ray absorptiometry. Analyses of serum parathyroid hormone, calcium, phosphate and osteocalcin concentrations suggested that the effects on skeletal growth were not related to alterations in calcium and phosphate homeostasis or a primary defect in bone formation. These findings suggest that long-term food restriction delays skeletal development in male rhesus monkeys while allowing the development of a reduced but otherwise normal skeleton.