How can I tell a guinea pig’s sex?

Telling a guinea pig’s sex mainly uses these points. A male’s genitals (penis and testes) sit farther from the anus, while a female’s vaginal opening is close to the anus with a smaller gap.

In adult or near-adult males you can directly see two small testicles near the genitals, below the tail base. Although not always, hair between the genitals and anus often marks a male, while a female has none.