During pregnancy and lactation, the maternal body undergoes many changes in the regulation of appetite, body weight, and glucose homeostasis to deal with the metabolic demands of the growing fetus and subsequent demands of providing milk for offspring. The aim of the current study was to investigate the consequences of one reproductive cycle of pregnancy and lactation on the long-term regulation of energy homeostasis. After weaning of pups, reproductively experienced (RE) mice maintained a higher body weight compared with age-matched control mice. Although there was no difference in daily food intake or the feeding response to exogenous leptin administration, RE mice were less active than age-matched control mice as measured by average daily x + y beam breaks or average daily ambulatory distance. RE and age-matched controls were also subjected to either a high-fat diet or control diet for 6 weeks to determine if experiencing a major challenge to energy homeostasis such as pregnancy and lactation leads to increased susceptibility to a second challenge to this system. Although both RE and control mice gained a similar amount of body weight on the high-fat diet, only the RE mice had impaired glucose tolerance when consuming the high-fat diet, thus demonstrating an increased susceptibility to the negative consequences of a high-fat diet after pregnancy and lactation. Overall, these data indicate that pregnancy and lactation have long-term consequences on energy homeostasis in mothers.