Instructions
Hold the cat gently and lift its tail to look at the genitals.
Locate the anus. In a female cat, directly below the anus is a vertical slit, the vulva, which is almost joined to the anus, creating an "i". In the male, about 1 1/4 inch below the anus is an opening to the prepuce or foreskin, with the remains of the scrotum above it. You might have to lift the cat's hindquarters for a clearer view. In a kitten the anus and prepuce appear as two dots with the scrotum in between.
Keep in mind that because there are only two choices, male or female, and because it's easier to determine the female sex, you can use the process of elimination. If there is no vulva the cat is male; if there is, it's female.
How to Tell a Fixed Male Cat From a Female
Neutering or castrating a male cat involves making small incisions in the scrotum and removing the testes. Typically, there is no need for sutures, but your veterinarian will determine if they are necessary. Neutering is usually performed between the age of 4 and 6 months to prevent unwanted male cat behaviors such as spraying. Once the skin of the scrotum has healed, it can be tricky for an untrained eye to determine the sex of a cat.