Among its many proposed functions, neuropeptide Y (NPY) is thought to modulate the hypothalamic-pituitary axis. Specifically, increased hypothalamic NPY signaling may be critical in mediating the neuroendocrine response to fasting. To determine the consequences of NPY deficiency on endocrine physiology, multiple hormones were quantitated in wildtype and NPY-knockout mice under fed and fasted conditions. Serum concentrations of leptin, corticosterone, thyroxine, and testosterone were normal in NPY-knockout males fed ad libitum. A 48-hour fast resulted in a 50% reduction in leptin, a 60% reduction in thyroxine, a 75% reduction in testosterone, and a 12-fold increase in corticosterone in both wildtype and NPY-knockout mice. Fasting also increased the estrous cycle length by 3 days in both wildtype and NPY-deficient female mice. We conclude that NPY is not essential for appropriate function of the gonadotropic, thyrotropic, or corticotropic axes under ad lib fed conditions or in response to acute fasting.