In my limited experience, roughly a quarter of patients who go to see a Urologist are women. Women get incontinence, kidney stones, kidney cancer, etc. just like men so there is certainly a role for women in the field if you assume that people like to go to Doctors of the same gender.
In terms of interest in Urology, the last statistic I heard was that roughly 4% of practicing Urologists are women and 15% of Urology residents are women. This year there were 70 women who matched in Urology and 176 men who matched. The match rate for both sexes was about 60%. Clearly it is becoming a more appealing specialty for women and it is unclear whether or how that will change the field.