The overrepresentation of individuals with an intellectual disability (ID) in the criminal justice system is an established phenomenon. Recently there has been an increased focus in the literature on risk assessment of offenders with an ID. A supplemental guide to the HCR-20 (Webster, Douglas, Eaves, & Hart, 199732. Webster , C. D. , Douglas , K. S. , Eaves , D. and Hart , S. D. 1997 . HCR-20: Assessing risk for violence, Version 2 , Burnaby, Canada : Mental Health, Law, and Policy Institute, Simon Fraser University . View all references) for offenders with ID was proposed to increase the standardization and reliability of risk assessment for ID offenders. The current project empirically evaluated the validity of these adaptive recommendations in a sample of 59 community-based ID offenders with a history of violent offending. By employing a retrospective approach, this study examined differences in the relationship between predicted risk and actual reoffending over a minimum of two years, as assessed by using the HCR-20 and HCR-20 with ID Supplement. Their predictive validity was also compared to that of the Violence Risk Appraisal Guide (VRAG; Quinsey, Harris, Rice, & Cormier, 1998). Predictive validity was generally good. Although statistical significance could not be determined, use of the ID Supplement resulted in a small improvement in predictive validity relative to the HCR-20 and VRAG. Implications of the findings for practitioners and recommendations for further research are discussed.