The urogenital sinus is a body part of a human or other placental only present in the development of the urinary and reproductive organs.

The phallic portion gives rise to the spongy (bulbar) part of the urethra and the urethral glands (Littré's).

In females, the pelvic part of the UG sinus gives rise to the sinovaginal bulbs, structures that will eventually form the inferior two thirds of the vagina.

This process begins when the lower tip of the paramesonephric ducts, the structures that will eventually form the uterus and vaginal fornices, come in contact with the UG sinus.

A urogenital sinus anomaly is also a rare birth defect in women where the urethra and vagina both open into a common channel.