Examining the use of deviant fantasies by sexual offenders and encouraging the gradual replacement of these fantasies with appropriate ones is a common practice in the treatment of sexual offenders. It is a practice based on the assumption that sexual offenders use deviant masturbatory fantasies prior to and after committing sexual offenses. The data to support this assumption are limited. Of the 82 participants in this study, 57 were in treatment for sexual assaults against children. Twenty-five participants were in treatment for exhibitionistic offenses. A questionnaire was used to ask participants to provide information about the nature of their offense, the number and type of victims they had (male or female), duration of time spent in treatment, and the number of polygraph examinations they took. The participants were asked to calculate the number of times they used deviant masturbatory fantasies before and after their first actual offense. They were also asked to estimate how many of these fantasies were directed toward a specific person or toward any person. The results indicate that the majority of child molesters experienced deviant masturbatory fantasies both prior and after their first hands-on offense. Child molesters reported having experienced significantly more fantasies after their first offense than prior to their first hands-on offense. The data were similar for exhibitionistic offenders: the majority of the offenders experienced deviant masturbatory fantasies both prior and after their first offense, with significantly more deviant fantasies taking place after the first offense. There was not a clear, predictable pattern in the use of fantasies about specific victims. It appears that the longer an offender spends in treatment, the more deviant fantasies he reports having experienced, specially after the first hands-on offenses. Further investigation is needed to examine whether the current findings apply to other categories of offenders. 1 table, 10 references