Kitten genitals are not as developed as adult cats, making gender determination a crapshoot. At first glance, even professionals find it tricky to distinguish a female kitten from a male. However, a few characteristic differences can be observed in kittens as young as five weeks old—genital spacing, coat color, and behavior—indicating their sex.
Don't disrupt the mother-kitten flow within the first few weeks of life. If a kitten is handled too much during this time, the mother may abandon it and stop nursing it altogether. So don't get too anxious to determine the sex of your kittens. Instead, wait until at least two weeks—or preferably longer—to start handling your kittens.
While assessing your kitten's gender, it is necessary to minimize stress. Start by picking him up, gently petting him, and snuggling him close to your body. Scratching his back right at the base of the tail may cause him to automatically lift it, giving you a bird's eye view of the parts in question. But if a kitten is standoffish or panicky, leave the inspection to a later date and bother a less sensitive member of the litter, instead.
Identifying the Genitals
At two weeks old, some breeders liken the appearance of kitten genitalia to punctuation marks. A female kitten's genitals will resemble an upside-down exclamation point, with the vertical vaginal slit sitting just below the anus and with very little spacing in between (when the cat is upside down and facing you). A male kitten's organ looks more like a colon, with the penis residing just below the anus and separated by enough space to accommodate his testicles. You may even be able to see small lumps in that space, which will grow as the kitten matures.
If, upon visual observation, every kitten looks the same to you, then pick one and gently place your finger and thumb on either side of the scrotum area (on a suspected boy). Palpate two small, hard, oval-shaped objects under the skin. These are the testes and they are almost impossible to hold—they slither away underneath your fingers. Obviously, if testes are present your kitten is male.
Another simpler, but less reliable, way to tell the sex of your kitten is by the color of its coat. Cats with three colors (sometimes called tortoiseshell cats) are almost always female. The chromosomal makeup of female cats is solely responsible for this coloration, so you can pretty much guarantee any calico cat is a girl. Orange or ginger-colored cats, however, are most often male (think of the iconic male tabby cats). Yet, this trait is not as reliable as the tri-colored trait, as only three-quarters of ginger-colored cats are male.
As kittens become bigger, they start to develop their unique personalities. Male "tom kittens" may start to roam as they approach sexual maturity. They may also become territorial, often spraying to establish their home base and ward off trespassers. Males are also more restless and aggressive.
Female kittens (sometimes as young as four months) may go into heat—vocalizing this "coming of age" with loud yowls and attention-seeking behavior. However, the earlier you spay or neuter your kitten (the standard recommendation is five to six months, but pediatric spay and neuter can happen at six to eight weeks) the less your cat will display these gender nuances.
Some people claim male cats are friendlier and more outgoing than females. But this difference is, by no means, universal and cat personalities are almost as varied as human personalities. So choose your pet by the connection you make upon first interaction, and pay less attention to its gender.