Changes in the volume and composition of body fluids are among the essential and limiting parameters both in health and illness. These parameters gain in importance with increasing age. Within the concept of a geriatric patient, disturbances in water and mineral metabolism are the cause of circulatory collapse, stroke, and further instability, falls and delirium. The body can, in the broad range of balance within internal environment, compensate for variations, however always for a limited length of time only, and this compensation ability decreases in particular in older age. Maintaining of water and mineral balance in the elderly is also complicated by polymorbidity. Frequent occurrence of cardiovascular diseases and decline in renal functions later in life results in reduced compensation abilities, which status must be rigorously considered. Besides polymorbidity, also polypragmasia in pharmacotherapy is very frequently encountered in relation to age-related disorders of water and electrolyte handling. Treatment with sedatives also suppresses the feeling of thirst, which results in rapid development of disturbances in water and mineral balance even after small insults, such as feverish illnesses and minor injuries. The knowledge of differences in diagnosing and treatment of water and ion imbalances in later life is becoming increasingly important, espe-cially with regard to the increasing share of older people in society. Key words: ageing - dehydration - electrolyte metabolism - mineral disorders.