Look under the tail
Males usually have a larger gap between the anus and genital opening
Males usually have a round genital opening
Males may have a visible scrotum if not neutered
Females usually have a smaller gap between the anus and genital opening
Females usually have a vertical slit-shaped genital opening
Compare the shape and spacing of the openings
Check for testicles in older kittens or adult males
Ask a veterinarian if you are unsure