The study involved the 184 male adjudicated sexual offenders committed at the time of data collection (1979-1982) to the Massachusetts Treatment Center for Sexually Dangerous Persons. The sample was comprised of repetitive offenders against adult women and children. The data source was the clinical file of each subject. Twelve subtypes were identified and compared with subtypes described the literature and with one rationally constructed typological system. Of the nine subtypes considered clinically distinct and meaningful, two manifested high aggression, four low aggression, and three moderate aggression. The study determined distinctive, recognizable subtypes of sexual offenders and established some degree of external and descriptive validity for them. Content issues regarding the subtypes as well as several of the issues and problems involved in classification research are discussed. 8 tables, 4 figures, 31 references. (Author abstract modified)