This is a common problem in newborn males and usually goes away within the first year of life. When the testicle drops into the scrotum (about the eighth month of pregnancy), a sac (the processus vaginalis) from the abdominal cavity travels along with the testicle. Fluid can then flow to the scrotum to surround the testicle. This sac usually closes and the fluid is absorbed.

When the sac closes and the fluid remains, this is called a noncommunicating hydrocele. This means that the scrotal sac can be compressed and the fluid will not flow back into the abdomen. This type of hydrocele is often found in newborns and the fluid will usually be absorbed with time. If the scrotal sac is compressed and the fluid slowly goes back up into the abdomen or if the hydrocele changes size, this is called a communicating hydrocele. This type of hydrocele usually appears smaller in the morning when the child wakes up and larger in the evening after activity. A communicating hydrocele shows that the sac or processus vaginalis is still open.