Assessing an individual s history of aggression is a common task in clinical and forensic mental health practice. Although several methods for quantifying aggression are available, the extent to which they yield comparable results is unclear. The aim of this study was to explore the convergent validity of three instruments assessing past aggression and violence (the Life History of Aggression, Aggression Scale [LHA-A], the Violence Rating Scale [VRS] and the Cormier-Lang System for Quantifying Criminal History-Violence Offences Index [CL-V]) using 87 offenders undergoing pre-sentence psychological and/or psychiatric evaluations for the criminal courts in Victoria, Australia. A frequency count of all violent offences recorded on official criminal records was also completed. Correlational analyses were used to explore the associations between the different indices. Results demonstrated convergent validity of the instruments, but suggest that the LHA-A most reliably quantifies the severity and frequency of past aggression.