The definition of prison bullying is when an individual is the victim of direct and/or indirect aggression happening on a weekly basis, by the same or different perpetrator(s). Single incidences of aggression can be viewed as bullying, particularly those that are severe and where the individual either believes or fears that they are at risk of future victimization by the same perpetrator or others. The sample consisted of 285 men and 217 women from 6 separate prison establishments. They were placed into one of four bully categories: pure bullies, bully/victims, pure victims, or not involved on the basis of a self-report behavioral checklist (Direct and Indirect Prisoner Behavior Checklist--DIPC). They also completed the Rathus Assertiveness Schedule (RAS) to measure assertiveness. Social assertiveness, argumentative and combativeness, and a willingness to converse with others were the three components of assertiveness among inmates. Results showed that men reported significantly higher overall assertiveness and social assertiveness scores than women. Pure victims scored significantly lower than the other bully categories on total assertiveness, supporting the prediction that those who were victimized would show the lowest levels of assertiveness of all bully categories. Pure bullies reported higher total assertiveness scores than the other bully categories. Bully/victims scored significantly higher on the argumentative and combative scale in comparison to the overall mean. There was a trend in the same direction for pure bullies. Those not involved scored significantly higher on social assertiveness. There was a trend for both bully/victims and pure victims to score lower on this component. These findings hold a number of implications for the development of bullying intervention programs, suggesting that assertiveness training may be an appropriate intervention for the victims of bullying. 2 tables, 27 references, appendix