The objective of this study was to estimate the circadian rhythm of urine formation and its association with the quality of life in incontinent women. 277 patients with complaints of urinary incontinence were analysed according to a specific protocol: urodynamic testing, transperineal ureterovesical segment ultrasonography, a 3-day frequency-volume (FV) chart. Subjects had to fill in a standardised quality of life questionnaire as well. Nocturia was defined as two or more micturitions per night calculated from the FV chart. The overall prevalence of nocturia was 39,7%. The nocturics were classified into one of the responsible pathophysiologic categories: nocturnal polyuria in 30%, a low functional bladder capacity in 23,6%, a combination of both in 24,5%, polyuria in 21,8% of the cases. In 54,5% of nocturics nocturia is due to change of physiological urine formation rhythm-nocturnal polyuria. So nocturnal polyuria is a frequent symptom among urinaryincontinent patients, with a negative impact on several aspects of the quality of life.