Four hundred and eighty-three consecutive women referred for videocystourethrography completed a structured questionnaire about their menstrual status and urinary symptoms. Women were included in the study if they were premenopausal, had a regular menstrual cycle and were not taking hormonal therapy. One hundred and thirty-three women satisfied the inclusion criteria of whom 55 (41%) complained that their urinary symptoms were cyclical. The times at which symptoms were said to be at their worst were reported by the women as follows: during a period (n = 20; 36%); just after a period (n = 4; 7%); middle of the month (n = 8; 15%); just before a period (n = 23; 42%). The prevalence of abnormal detrusor activity on videocystourethrography increased significantly with time from the last menstrual period (chi2 for trend = 6.56, P = 0.01) and might reflect increases in the circulating level of progesterone following ovulation. This study provides further indirect evidence that progesterone could have an adverse effect on female lower urinary tract function. In addition, it might be necessary to consider the stage within the menstrual cycle when interpreting the results of urodynamic investigation.