Anus, imperforate: A congenital malformation (a birth defect) in which the rectum is a blind alley (a cul-de-sac) and there is no anus.

The anus is imperforate in the sense that the normal perforation we call the anus is absent. The end of the intestinal tract has not made its way through the skin in the perineal area.

Imperforate anus occurs in 1 in about 5,000 newborn babies. It has to be corrected by surgery.

Imperforate anus is also known as anal atresia.