Nocturia is defined as waking one or more times to void during the period between going to bed with the intention of sleeping and waking with the intention of arising.The pathophysiology of nocturia is multifactorial and can be complex. Therefore it is important to adopt a systematic approach to identify the possible causal factors of nocturia and to treat them accordingly. Patients with nocturia can be categorized as having one of the following three disorders: (1) nocturnal polyuria (NP) in which the voided urine volume during the hours of sleep exceeds 35% of the 24-hr output, (2) low nocturnal bladder capacity (NBC) causing a nocturnal urinary volume greater than the bladder capacity, (3) or mixed nocturia, a combination of the preceding two categories.