Most of the studies have shown that serious inmate-on-staff assaults are relatively rare in prison. Rather, inmate-on-staff violence consists of minor physical assaults and psychological attacks. Although many studies have pointed out the factors that influence the professional practices of prison guards, very few have looked at the impact of violence on their work. We surveyed a sample of 132 provincial prison guards working in the Montreal area to establish the levels and the forms of intimidation they had experienced from inmates and to determine its impact on their professional practices. On the one hand, our results confirm the levels of inmate-on-staff violence found in previous studies. On the other, it appears that this violence changes some of their professional practices. Further studies are needed in order to validate the concept of professional practices of prison guards.