In patients during the agonal and pre-agonal phases, clinical symptoms of dehydration or fluid overload may occur. These symptoms have numerous physiological causes but can also be related to underlying diseases, medications administered to patients, or the type of therapy (chemo- and radiotherapy). Dehydration-related symptoms can affect almost all body systems and should be monitored by medical personnel, because disregarding them can lead to a deterioration in the patient’s quality of life and further complications. However, recent evidence has shown that patients may also benefit from dehydration in the final days of life. Laboratory parameters are a debated indicator of dehydration, and their importance should not be considered conclusive. Patients may also experience fluid overload in the terminal state, which also presents clinically. Excess water in the body can cause discomfort for the patient but may also have certain benefits, such as improved drug distribution in the body. Therefore, there is no consensus in favour of or against fluid administration in terminally ill patients.