Routine neutering of both male and female rabbits is strongly recommended unless you wish to breed.
Rabbits become sexually mature between 4 months (in smaller breeds) and 6-9 months (in larger breeds). It is recommended that young rabbits be separated into single sex groups at 16 weeks of age. Breeding is prevented by castration of male rabbits at about 5-6 months of age (once the testicles have descended), or spaying of female rabbits at about 6 months of age. Having your female rabbit spayed prevents uterine tumours later on in life. In some breeds the incidence of this cancer is over 80% in does over 5 years. Intact males are more prone to developing behavioral problems including fighting, biting and urine spraying. The urine may also become strong smelling.
Neutered rabbits are more prone to obesity as they grow older, so care must be taken not to allow overeating.