Energy expenditure as a factor in both the pathogenesis of cancer cachexia and in the clinical course of a malignancy has received relatively little attention in the oncology nursing literature. Nursing interventions that are done to influence nutritional status and day-to-day functional abilities of cancer patients may be compromised by alterations in energy requirements and availability of nutrients. Energy expenditure as one clinical manifestation of cancer and current measurement techniques for assessing energy expenditure are described. By becoming more familiar with the current state of knowledge of aberrations in energy expenditure that accompany cancer, nurses may be able to anticipate more accurately patterns of patient debility and to incorporate more refined strategies for assisting patients and families to cope with changes.