Optimal age for ovariohysterectomy or castration has not been defined in the scientific literature. Bitches and queens are significantly less likely to develop mammary neoplasia, which has a high incidence and potentially high morbidity and mortality, if spayed when young. Tom cats exhibit undesirable behaviors that preclude them being good pets and should be castrated young. There is no compelling reason to castrate male dogs when young unless it is needed to control reproductive behaviors or prevent indiscriminate breeding. Alternatives to surgical sterilization that may be available in the future include intratesticular injection and immunization against gonadotropin-releasing hormone.