A male kitten's penis sheath appears as a small circular dot, below the anus and clearly separated from it. A female kitten's vulva appears more like a slit and is closer to the anus.
Although kittens can be sexed even as newborns, it is better to wait until they are at least 3 weeks old, as too much handling at an early stage can cause the mother cat to reject her kittens. To view a kitten's genitals, place the kitten on a clean towel and gently lift its tail. Kittens older than 10 weeks of age are easier to sex as the male's testicles begin enlarging in the scrotal sac by that age.