Rape is recognized as the fastest growing crime in the United States, but little effort has been made to investigate developmental and enviromental factors that influence a rapist's behavior. Previous studies on rapists' characteristics and the obsessive-compulsive personality are reviewed. The sample selected for this study consisted of 60 male subjects classified into 3 groups: 21 mentally disordered sex offenders--group A whose members had first contact with the police through their arrests for rape; another 21 mentally disordered sex offenders--group B whose members had been arrested for felonies prior to the arrest for rape; and 18 volunteer nonoffenders. All subjects were heterosexual, between 18 and 35 years old, literate, and from family units that remained intact at least until their 13th birthdays. All were given the following tests in three sessions: the Minnesota Multiphasic Personality Inventory, the Sexual Knowledge and Attitudes Test, the Shipley Institute of Living Scale, and a supplemental questionnaire which explored environmental issues. The theory that group A sex offenders would exhibit excessive sexuality was only partially confirmed, although this group did appear to have more problems with heterosexual and interpersonal relationships. The group A rapist was closer to the nonoffender group in the statistical results and presented an impressive veneer of normality and youthfulness to the investigators. Both rapist groups expressed more conservative sexual attitudes and less accurate information concerning heterosexual issues than did the nonoffender group. All groups exhibited and above average intellectual capacity. Present treatment strategies that emphasize behavior modification and socialization are probably ineffective in reaching the alienated, secret life of the group A rapist personality, and indepth psychotherapy should be considered. The appendixes contain the testing instruments, statistical tables, Atascadero State Hospital (California) regulations for using patients as research subjects, and the project proposal submitted to the hospital. Forty-one references are included. (Author abstract modified)