Paraphilia refers to occasional concomitant disorders of pervasive developmental disorder(PDD). When a restricted interest of PDD is focused on a sexual object, paraphilia may be develop as a problematic symptom. However, having this concomitant disorder does not always result in criminal behavior. When the social interactivity of a particular patient with PDD is severely impaired, paraphilia could lead to a sex crime. Because pedophilia targets sacrifice innocent and defenseless children, it is critical to prevent such sex crimes by understanding the psychopathology of PDD with paraphilia, especially pedophilia. Two cases of male adolescents with high-functioning PDD and pedophilia were reported; one ended up committing a serious crime, and the other controlled his sexual impulse. The psychopathology of these two cases was similar; however, the outcome turned out to be quite different. The similarity and dissimilarity of these two cases were analyzed. We came to a conclusion that early intervention could be a key to prevent the development of criminal sexual behavior in PDD with paraphilia (pedophilia). Both patients became aware of pedophilia during adolescence and developed a depressive state at the time of consulting our clinic. In the first case, the patient stabbed a woman with a knife. He could not respect other people, including women he was sexually interested in and has always been preoccupied with his own peculiar ideas. He did not listen to other people's opinions and his abnormal thoughts had never been corrected because of his lack of ability to form interpersonal relationships. The second patient could control his sexual impulse. He has an ability to sympathize with the child he is sexually interested in and has confronted his sexual impulses. He could build interpersonal relationship with others and listen to other people's opinions. He made an effort to manage his sexual impulses positively through individual psychotherapy. He was diagnosed at the age of two years and started rehabilitation training soon after. He had some experiences of consulting people when he was in trouble. In the treatment and correctional education of pedophilia, some sort of special care regarding the characteristics of PDD is indispensable; e.g., pointing-out and explaining unacceptable behavior repeatedly, teaching the correct action concretely, and changing the pathological sexual preference into a constructive one, etc. These therapeutic approaches are quite different from controlling paraphilia without PDD. PDD adolescents with impaired social interactivity could be further helper if they are diagnosed at an earlier stage of their lives and managed appropriately. A sense of being accepted by others and also experiences of mutual interaction with others are particularly important for them. Professionals should be aware that an early and proper intervention method could prevent the later development of criminal behavior in PDD adolescents who suffer from a sense of incompatibility with others because of concomitant paraphilia.