ABSTRACT Background Social identity is a well‐established theoretical concept within psychological research; however, the role of criminal social identity has received far less research attention. One salient reason for the limited research relating to the concept of criminal social identity is the absence of a specific measure. Aim To develop and test the construct validity of a new measure of criminal social identity (MCSI) and to provide additional evidence relating to Cameron's three‐factor conceptualisation of social identity. Method The eight‐item MCSI was used to collect data from recidivists incarcerated in high‐security prison ( N = 312) to assess criminal social identification. These data were subjected to confirmatory factor analysis. Results Three alternative models of criminal social identity were specified and tested in Mplus 6, and results revealed that the data were best explained by a three‐factor model of criminal social identity (cognitive centrality, in‐group affect and in‐group ties). Conclusion The current study is important in terms of future research in criminology and psychology because the MCSI provides the first reliable MCSI, which was developed and validated on a relatively large recidivistic prison sample.