In the past decades, Europe has been shocked repeatedly by terrorist crimes. This has led to an influx of suspects and convicts of terrorism in the prison system. The aim of this study is to provide insight into socio-demographic, psychopathological and criminal background characteristics of convicted violent extremists. Retrospective analyses were conducted on primary source data from 82 convicts in Dutch prison terrorism wings. Results showed that violent extremists are a heterogeneous group regarding socio-demographic characteristics. About 60% of the population had previously been convicted of ordinary crimes and a third suffered from a mental disorder. To gain more insight into violent extremists, additional research is needed into motivational and other risk factors. The latter is a necessary step to improve the identification, risk assessment, and effective treatment of violent extremists.