The breeding season for ferrets in Victoria is from August to March. Both jills and hobs have a clearly defined, breeding season, marked by the jill's vulva swelling up to about 12mm in diameter (it is ordinarily less than 2mm m length) and the hob's testicles descend into the scrotum. Mating takes several hours and appears quite violent to bystanders. Gestation time is 42 days, after which an average litter of 6-10 kits are born. They will be blind and deaf for about five weeks, weaning takes place, between 6 and 8 weeks.
Jills which are not mated stand about a 90% chance of developing "prolonged oestrus disease" which is a fatal form of aplastic anaemia. It is sometimes called "fading syndrome", as she may take 6 weeks to gradually lose condition and die. It can be easily avoided by having her speyed (i.e. desexed), by mating her with a vasectomised hob, or by giving her hormone injections that can be obtained from a vet. The latter two only solve the problem for a short amount of time, after which she will require mating again; if she comes into season again or more injections.