Research utilizing psychometric instruments to assess personality characteristics of sex offenders is reviewed. A methodological shortcoming of this research is the frequent use of the MMPI. It is argued that this test was originally developed as a measure of types of psychopathology and has not been validated as a personality test. Studies using tests other than the MMPI have seldom controlled for institutionalization and impression management. Further, little attention has been paid to criminal history, making it difficult to conclude that the current offense is representative of past behavior. In the case of child molesting, there has been a failure to specify and/or control for age and sex of victim and degree of force used. Results suggest that men who engage in rape and child molesting are guilt-ridden individuals who inhibit aggression, but these findings are tentative because of the aforementioned methodological problems.