The effect of a high-fat diet on growth, sexual maturation, and developmental changes in serum levels of estradiol (E2), growth hormone (GH), somatomedin-C (Sm-C), and insulin were examined in outdoor-housed premenarchial rhesus monkeys. From 16 to 32 months of age, females were fed either a high-fat diet (HFD, N = 5) with 31% calories from fat or a control diet (commercial laboratory chow, N = 10) with 12% of the calories from fat. Maintenance on a HFD did not accelerate physical growth, as all animals exhibited similar increments in body weight, crown-rump length, and weight/height ratios. In contrast, the HFD group exhibited an earlier onset of perineal swelling and menarche despite lower body weights during that time. Moreover, 80% of the HFD animals exhibited an early first ovulation (31-32 months of age) compared with 40% of control animals. These reproductive changes were associated with significant differences in the endocrine profiles of HFD animals. Fasting serum levels of insulin were significantly elevated within 2 months of diet treatment and remained elevated throughout the study period. Levels of Sm-C were elevated relative to those of controls after 3 months of diet treatment, but not thereafter. Serum GH increased after 6 months on the HFD and, overall, concentrations were higher in HFD animals. A significant rise in E2 was observed after only 45 days on the HFD treatment. These concentrations did not differ from 18 to 21 months of age but again were elevated at 27 months in the HFD females. Since these endocrine and physical changes associated with reproductive physiology occurred in the absence of enhanced growth, these data suggest that a high-fat diet may influence the rate of sexual maturation through changes in certain metabolic factors which may act on the developing neuroendocrine system.