A total of 3,972 inmates provided information about the offenses related to their current Federal prison sentences. More than four of five Federal offenders were violent offenders. Violent offenders were a heterogeneous group. Sex offenders and robbers were dissimilar on most of the study measures; the generally violent group (assaults, weapons, death of victims) also differed from both the sex and robbery offender groups on many of the survey indicators. Robbers and break-and-enter offenders displayed the most troublesome behavior inside prison and exhibited more extensive criminal histories before incarceration. Those who generated the greatest fear in the public (sex offenders and those who kill their victims) actually displayed the most signs of cooperation, treatment motivation, and a lower risk of recidivism. Findings indicated the need for more detailed breakdowns of offense types when describing Federal offender populations and for avoiding using the violence/nonviolence dichotomy as the main division of offense type. Tables, figures, and 3 reference notes