How do you tell male from female ferrets?

The most obvious sign - look at the ferret's underside - if you see what looks like a belly button - it's a male

Male ferrets have a 'belly button' :) Actually, many people think that their ferret has a pronounced outie belly button, only to find out it is the male ferret's penis. It actually is in the lower part of the abdomen on the underside of the male ferret, while the female has her vulva much closer to the anus - just a few millimeters away, compared to several centimeters between the penis and anus of the male ferret.

A way to determine gender - turn your ferret over on his/her back. A female will have an opening (vulva) directly above the anal opening. For a male look about half way between ribcage and the tail and what can be mistaken for a the "belly button", it's not a belly button, but a penis.

Some major physical differences between male and female ferrets, first being size, males always larger that females. Female ferrets usually grow to be 12 -16 inches long, give or take a few for the tail, while male ferrets average a 1 1/2 - 2 feet in length with a heavier build. Another way of telling is by the head shape. Ferrets' heads are wedge, or 'V' shaped, male ferret's head is much wider of an angle than the female - female's noses are more pointed. Male ferrets can be much more odorous than the female due to size and hormones.

It's the same with humans, just gotta look more carefully. And females act differently then males.

Adult female ferrets are about 3 inches shorter than adult male ferrets. Male ferrets also have longer, thinner noses, and more wide-set ears.

The most obvious way to tell is just to look, though. Female ferrets appear to have nothing down there, while male ferrets do.