A large body of literature has examined the cause and treatment of aggressive behavior in prisons, but heterogeneity in the outcome measures used has led to difficulties comparing outcomes across studies. This systematic review aims to identify a Core Outcome Set for measuring aggression in prisons. Studies were eligible for inclusion if they measured aggressive behavior in adult male prisoners, described original research, and were in English. A systematic search of Medline, PubMed, PsycInfo, CINAHL and Cochrane databases to 7 March 2022 was conducted. Risk of bias was assessed using the QUADAS-2 method. The titles and abstracts of 19,619 records were screened, with 641 reports identified for full-text examination. From these reports, 283 studies with a total of 1,402,931 prisoners were included. These studies were predominantly published from 2000 onwards, published in North America, used a cross-sectional design, and included a single method to measure aggressive behavior. The studi