To study the sexual assault of young children, two research bases (differing by unit of count) were extracted from the 1991 through 1996 NIBRS master files. One base summarized the information for each of the 60,991 victims of sexual assault, the incident characteristics, and (where available) information on their offender(s). The second base compiled information for each of the 57,762 victim-identified offenders in sexual assault incidents, their victims, and related incident characteristics.