About two thirds of undescended testes descend on their own by 4 months of age in full-term infants or, for premature infants, by 4 months after the date they would have been born if they were not premature.

Most of the time, a boy's testicles descend into the scrotum by the time he is 6 months old.

In most cases, the testicles (or testes) descend into the scrotal sac during foetal development. In 3% of newborn boys, the testes may not have descended at birth, but could do so over the first 6 months of life. If they haven’t done so, a consultation with a specialist paediatric urologist is advisable.

The testicles travel down into the scrotum between 28 and 40 weeks gestation. At birth, 2 to 3 percent of boys will have one testicle that is not in the scrotum. The final descent of the testis may take up to six months after birth, but usually occurs within three months of birth.

Recent evidence suggests that most spontaneous descent occurs by six months of age. Damage to the germ cells, which give rise to sperm later in life, has been noted to occur as early as 12 to 18 months.