My son is 13 and his testicles are small is this because they havn't dropped or because he had a hernia when he was 4?

Testes: Either way, he should be checked by a urologist, especially if he has not started puberty.

Unknown : Sounds like the testicles have dropped, but are small. While there is a possibility it is due to a hernia repair at age four, it is very unlikely. In fact he may have a variation of normal anatomy. Check with your pediatrician to be sure.