Nocturia is defined by the International Continence Society (ICS) as “the complaint that the individual has to wake at night one or more times for voiding (i.e. to urinate).”

Its causes are varied and, in many patients, difficult to discern.

Diagnosing nocturia requires knowing the patient's nocturnal urine volume (NUV). The ICS defines NUV as “the total volume of urine passed between the time the individual goes to bed with the intention of sleeping and the time of waking with the intention of rising.”

Thus, NUV excludes the last void before going to bed, but includes the first morning void if the urge to urinate woke the patient. Although not every patient needs treatment, most people seek treatment for severe nocturia, waking up to void more than 2-3 times per night. The amount of sleep a patient gets, and the amount they intend to get, are also considered in a diagnosis. The term is derived from Latin nox, night, and Greek [τα] ούρα, urine.