How can you tell if your chinchilla is male or female? Well, it's actually very simple. All you need to do is hold your chinchilla with one hand, while lifting the tail with the other. You should clearly see the anus and external genitalia of the chinchilla. Some people recommend holding your chinchilla upside down, but they tend to struggle and fuss over this, and you really don't need to anyhow. Once you have lifted the tail and can see the anus, you will notice that the anus either looks like it has a cleft, or the anus and genitals look like two separate orifices.

If the anus and genitals look like a small cleft, your chinchilla is a female.

If there are two separate orifices, the chinchilla is a male.

Check out these two pictures, courtesy of Anubis Chinchillas

That's a male chinchilla on the left,  and a female on the right. 

Once you know what to look for, you will be able to sex a chinchilla in seconds, and even be able to sex newborn chinchillas easily!