Determining the sex of a kitten may be difficult especially before about 8 weeks of age. The male and the female kitten's genitalia look remarkably similar. If kittens of both sexes are available to compare, it makes the process easier and more likely to be correct. In the male kitten, the scrotum is located below the anus and above the back of the hind legs. The testicles are descended into the scrotum presumably at the time of birth. The cat's penis is immediately below the scrotum and projects behind the cat and is normally not visible. The penis is enclosed in the prepuce. The female kitten's vulva is located below the anus and above the back legs. The vulva appears more as a slit than the more circular appearance of the prepuce in the male.

Males and females both have nipples.