The urodynamic changes in 10 bitches up to 18 months after they had undergone ovariectomy were investigated. There were significant decreases in the maximum urethral closure pressure, the functional urethral length and the total integrated pressure profile 18 months after spaying, resulting in a caudal shift of the urethral profile, and a deterioration of urethral closure function. Each urethral pressure profile was divided into three equal sections; the mean cranial and middle integrated pressure decreased significantly and consistently over the 18-month observation period whereas the caudal integrated pressure increased.