To describe the normal values for nocturnal urine production and its determinants, as well as the relation between nocturnal urine production and voiding frequency.

Data were collected from 1688 men aged 50 to 78 years without bladder or prostate cancer, radical prostatectomy, neurogenic bladder dysfunction, or negative advice from their general practitioner. Measurements included self-administered questionnaires, a 3-day frequency-volume chart, transrectal ultrasonography of the prostate, uroflowmetry, and postvoid residual urine volume measurement. The mean nocturnal urine production was computed from the frequency-volume charts. Linear regression analyses were performed to determine associated factors for nocturnal urine production. Areas under the receiver operating characteristic curves were used to describe the discriminative value of nocturnal urine production on nocturnal voiding frequency. A cutoff value for “increased” nocturnal urine production was defined using logistic regression analysis.

The nocturnal urine production was 60.6 mL/hr for the total study population; it increased with age and was significantly higher in men with 24-hour polyuria. Nocturnal urine production was on average higher in men with increased nocturnal voiding frequency, but had only a reasonable discriminative value on nocturnal voiding frequency (areas under receiver operating characteristic curve of 0.71 and 0.76). Nocturnal urine production exceeding 90 mL/hr is suggested as abnormal.

On average, nocturnal voiding frequency is indicative of nocturnal urine production. However, nocturnal urine production is only a modest discriminator for increased nocturnal voiding frequency. Therefore, the use of nocturnal urine production as an explanatory variable for nocturnal voiding frequency in daily practice is of little value.