Micropenis is an unusually small penis. A common criterion is a dorsal (measured on top) erect penile length of at least 2.5 standard deviations smaller than the mean human penis size, or smaller than about 7cm (3 inches) for an adult when compared to an average erection of 12.5cm (5 inches). The condition is usually recognized shortly after birth. The term is most often used medically when the rest of the penis, scrotum, and perineum are without ambiguity, such as hypospadias. Micropenis occurs in about 0.6% of males.
Because hormone treatment rarely achieves average size, several surgical techniques similar to phalloplasty for penis enlargement have been devised and performed; but they are not generally considered successful enough to be widely adopted and are rarely performed in childhood.
In extreme cases of micropenis, there is barely any shaft, and the glans appears to sit almost on the pubic skin. From the 1960s until the late 1970s, it was common for sex reassignment and surgery to be recommended. This was especially likely if evidence suggested that response to additional testosterone and pubertal testosterone would be poor. If parents accepted, the boy would be reassigned and renamed as a girl, and surgery performed to remove the testes and construct an artificial vagina. This was based on three now questioned assumptions:
gender identity and sex differences were solely a matter of social learning rather than biology.
a male with a penis too small to put into a vagina could not find a satisfactory social and sexual place in society.
a functionally acceptable vagina could be constructed surgically.