Congenital abnormalities of the female canine reproductive tract are uncommonly seen in veterinary practice, with reported occurrence in 0.02–0.05% of the canine population [1]. An imperforate hymen results from failure of the caudal paramesonephric ducts to fuse with the urogenital sinus, leading to an obstruction located between the vagina and the vestibule, just cranial to the opening of the urethra [1, 2]. If vaginal outflow is completely obstructed, accumulation of normal vaginal secretions will result in its distention, which is known as hydrocolpos [2]. Dogs presenting with imperforate hymen often have a history of infertility or clinical signs secondary to vaginal dilation, including dysuria, dyschezia, and abdominal distention [1, 3–5]. This case report describes a case of hydrocolpos secondary to an imperforate hymen resulting in a novel presenting clinical sign: perineal protrusion.