PRISM: Promoting Risk Intervention by Situational Management (Johnstone & Cooke, 2008) provides a systematic process for evaluating a range of situational risk factors known to influence institutional violence in prisons and secure hospital settings. This paper reports on findings from the first multiple case-study evaluation using this protocol. We applied PRISM in the Scottish Prison Service (SPS). The SPS is a modern prison system. It respects prisoners’ human rights, maintains order and control via humane and dignified means, and works towards the rehabilitation of prisoners and reducing reoffending rates overall. The SPS comprises a national headquarters where relevant policies and protocols are derived but governors and senior management teams are based within the local prisons to ensure the effective running of the organisation. While the SPS can boast decreasing rates of serious violence, there are significant variations across sites. We used PRISM to explore the relevance of situational risk factors to understanding these variations. Results suggested that the protocol was a promising paradigm for assessing risk factors unique to each site as well as showing utility for exposing problems related to the national policies and practices. The risk assessment led to a range of risk management interventions being proposed. The implications of the findings are discussed.