The authors explain that recent legislation in many States has made it possible for certain sex offenders to be held in civil commitment at the close of their incarceration period. Sex offenders who are deemed a continued threat to society may be held in civil commitment upon the petition of the attorney general of the State in which the offender was incarcerated or the prosecutor in the county in which the offender was prosecuted. The authors reveal that there is a scarcity of research involving the characteristics of such civilly committed sexually violent predators. In order to obtain more information about this category of offender, the authors examined the legal files of 120 sexual offenders who had been petitioned for civil commitment in the State of Arizona. The legal files contained information regarding correctional records, mental health evaluations, and demographic data. This data on the 120 Arizona offenders were then compared to similarly petitioned sex offenders in Minnesota, which was provided by a previous study. Numerous similarities and some differences were noted in the comparison of the two groups of civilly committed sex offenders. Among the main differences were racial characteristics, which is most likely a function of the different racial and ethnic composition in the two States. Another difference was age of offender, with the Arizona population of offenders being somewhat older than the Minnesota offenders. Among the main similarities noted between the two groups were a history of substance abuse problems and a high rate of personality disorders. These findings indicate a need for comprehensive substance abuse and mental illness treatment for incarcerated sex offenders. Tables, references