You can determine your ferret's sex by examining its external genitalia.
Male ferrets have a ventral abdominal penis and are generally larger than females.
Most ferrets, whether male or female, are neutered at an early age before they reach the pet market. This results in a pet that is more placid, less moody and less at risk for reproductive diseases. Intact females must be spayed or bred to prevent fatal estrogen toxicity. Also at an early age their anal scent glands are removed. This results in a reduction of their natural odor, making them more desirable as pets.