Castration has been documented throughout history as occurring for a variety of social, punishment, and medical reasons. Both physical and chemical castration are currently being debated with respect to sex offenders, because both the public and legislators are calling for actions to reduce sex offenses. Chemical castration has been proposed as a reversible alternative. Its effectiveness, side effects, risks, and recidivism rates have been studied extensively over the last 25 years. In contrast, physical castration has been used mainly in Europe, has not been rigorously studied, and remains a highly controversial and irreversible procedure. However, reported recidivism rates are substantially better than those for chemical castration. Treatment that lowers testosterone offers a way to reduce and control and deviant sexual fantasies and urges of hard-core offenders, although such biological interventions are only part of the treatment plan and do not solve the problem of sexual violence. In addition, several legal and ethical issues need to be resolved. Therefore, guidelines are needed for further study regarding the potential benefits of physical or chemical castration. Tables and 46 references (Author abstract modified)