This rare malformation occurs chiefly in males. In this anomaly the posterior wall of the urinary bladder protrudes through a defect in the anterior abdominal wall below the umbilicus. The trigone of the bladder and ureteric orifices are exposed. In males exstrophy of the bladder is always associate with epispadias (an anomaly of the penis, which described in detail later in this chapter). If the affected child is a female, the exstrophy of bladder is associated with a -bifid clitoris. In both sexes there is a wide separation of the pubic bones at the pubic symphysis. Exstrophy of the urinary bladder results from the failure of migration of mesenchyme between the surface ectoderm and cloaca. Consequently, the thin epidermis and anterior bladder wall rupture. The disorganization of growth in this region leads to separation of the pubic bones and anomalies of the development of the penis (or clitoris).