Nocturia is commonly referred to urologists, but the mechanisms underlying the problem, together with the appropriate clinical assessment and management, may lie outside the ordinary scope of the specialty. Some serious conditions may manifest nocturia as an early feature, often as a consequence of nocturnal polyuria (NP). Voiding frequency is influenced by rate of urine output, reservoir capacity of the bladder, lower urinary tract (LUT) sensation and psychological response. Polyuria can result from polydipsia or endocrine dysfunction. NP can result from endogenous fluid and solute shifts, cardiovascular and autonomic disease, obstructive sleep apnoea, and chronic kidney disease. Nocturia without polyuria occurs in the presence of LUT pathology, pelvic masses and sleep disturbance. Drug intake can contribute to, or counteract, each of these problems. In assessing nocturia, clinicians need to consider an undiagnosed serious condition that may manifest nocturia as an early feature, or suboptimal management of a known condition. The frequency-volume chart is a key tool in categorizing the basis of nocturia, identifying those patients with global polyuria or NP, for whom involvement of other specialties is often necessary for assessment and management. Treatment should be directed at the cause of the problem, with a view to improving long-term health and health-related quality of life. Simple steps should be undertaken by all patients, including improvement of the sleep environment and behaviour modification. Evaluation of treatment response requires objective data to corroborate subjective impressions. Some mechanisms of nocturia do not reliably improve with treatment, leading to refractory symptoms.