Bivariate and multivariate statistical analyses were conducted, with different models of self-legitimacy being tested to determine antecedents of self-legitimacy best suited for the Slovenian prison environment. Also, the impact of prison workers’ self-legitimacy on their support for different treatment of prisoners and the willingness to use force was analysed. Results show that traditional models for measuring self-legitimacy are not best suited for the Slovenian prison environment. Feelings of obligation toward prisoners, prison workers’ subculture, and professional competencies were identified as the strongest predictors of prison workers’ self-legitimacy. Self-legitimacy had no impact on prison workers’ support for the rehabilitation of prisoners or harsh treatment but influenced prison staff’s willingness to use force upon prisoners. Comparative analysis revealed statistically significant differences in the perception of self-legitimacy between prison officers and other prison workers. Comparing prison workers’ perceptions of their legitimacy in two time periods confirmed the unstable nature of legitimacy, as differences were observed in self-legitimacy and antecedents.