Some experts think 80 percent of all rapes and other sex crimes go unreported because the victims are embarrassed or fear social stigma. Moreover, although clearance rates for reported sex crimes are high, perhaps 30 percent of those convicted of sex crimes are not imprisoned or given criminal records. Thus, the proportion of known sexual offenders is may not be large enough to be helpful to those seeking ways to deal with sexual crime. Further research into sex crime should take into account unreported rapes or cases where information on the suspect or criminal is incomplete. However, the criminal justice system itself, lacking the unity and competence ascribed to it, often produces faulty criminal histories. The problem of dangerousness is relatively unimportant in relation to the identified sexual offenders. Thus, the difficulties of introducing new measures are likely to outweigh the benefits. Tables are included.