Aphallia is a medical condition in which the phallus (penis or clitoris) is congenitally absent. Aphallia is a rare birth defect of unknown cause. It is not linked to deficient hormone amounts or action, but rather to a failure of the fetal genital tubercle to form between 3 and 6 weeks after conception. The urethra of an affected child opens on the perineum. Although aphallia can occur in both males and females, it is considered a substantially more troublesome problem in a male, and has in the past sometimes been considered justification for assigning and rearing a genetically male infant as a girl.