To provide an overview of issues central to hydration in an oncology population while highlighting recent advances and publications in the clinical and scientific literature.Dehydration accounts for a significant number of unplanned visits to cancer clinics and emergency rooms. The decision to provide or withhold fluid in patients with terminal cancer is strongly influenced by subjective beliefs and the decision to use of hydration at the end of life should be individualized. Chronic dehydration may play a role in the pathogenesis of cancer.Cancer patients are at high risk for dehydration from both the disease and the treatment. Treating physicians should have a low threshold for providing additional fluids to prevent dehydration. For patients at the end of life, hydration may be indicated in select patients.