Because decreased caloric and nutrient intake can complicate the course of both mild and serious illness, parenteral nutrition (PN) is an important feeding modality for patients unable to receive adequate enteral nutrition. Although the effectiveness of PN has not been proven in animals, human studies have shown that using PN in appropriately selected cases can improve clinical outcome, reduce hospitalization time, and even reduce the overall cost of patient care. PN formulations for animals are readily available through pharmacies. This article provides practitioners with basic information on calculating and using PN in patients. Information is also provided on monitoring patients receiving PN as well as ways to identify and overcome common complications in animals receiving PN.