Nocturia is common in the elderly population and, aside from being a nuisance, it is associated with morbidity and mortality. Nocturia results from the complex interactions of several factors: changes in the urinary system and renal function with aging, the effects of sleep on renal function, changes in sleeping patterns associated with aging, and the presence of concurrent diseases and medications. Nocturia in the elderly can be caused by many conditions; a common cause is the syndrome of nocturnal polyuria. Although the pathophysiology of nocturnal polyuria remains obscure, some investigators believe that low night-time levels of antidiuretic hormone are involved. Proper management of nocturia requires identification of the specific underlying causes. This Review provides an overview of the mechanisms, evaluation and treatment of nocturia for the practicing nephrologist.