Offense versatility was the more likely tendency across the sample. Committed and observed offenders did not differ. Although predominantly versatile, child molesters were significantly more likely than rapists to specialize in sexual offenses, and were also more likely to specialize in child molestation. Consistent with previous research with sexual offenders, both measures of offense specialization revealed substantial difference between child molesters and rapists. As expected, rapists had more versatile criminal records. The extent to which persistent sexual offenders specialize in sexual offenses, or the extent to which they also engage in nonsexual offenses, has only recently become the subject of empirical inquiry. This study explored the extent of both tendencies (specialization and versatility) in the criminal histories of 572 adult male sexual offenders referred to civil commitment. The specialization threshold and the diversity index were used to compare offender subgroups by referral status. Tables, notes, and references