The castration of dogs is an amputation covered by Section 6 (1) of the Animal Protection Law in Germany. Apart from the general indications given by veterinary medicine, castration of an animal is a potential method of animal behaviour therapy. However, the highly variable, individual effects of castration on behaviour require detailed diagnosis by the veterinarian. Castration appears to exert its strongest influence on sexually dimorphic behaviour patterns in male dogs, e.g. status- related aggression, urine marking, mounting, house-soiling problems, and roaming. An indication to castrate a bitch is maternal aggression. When evaluating the effects of castration, one should always consider individual circumstances, such as learning experience (for example in the case of "experienced copulators"), age, and pack behaviour (if there is more than one dog in the household). Additional benefits of castration include a reduction in the dog's general activity level, decreased preparatory arousal and a decline in the dog's ability to focus its attention fully on the target of attack. As a result, it is much easier for the owner to disrupt and manage or control the dog's agonistic intentions. However, castration is not the ultimate remedy in dog-handling. Any decision in this respect should be based on a precise behaviour- related indication. Otherwise, such surgery may well violate the Animal Protection Law.