Background: Among mainstream offenders, the severe personality disorder of psychopathy has considerable importance as a construct. The disorder has long been associated with failure to make treatment progress. Previous work has identified that psychopathy as a disorder occurs in samples of offenders with intellectual disability (ID), and suggests that the "Psychopathy Checklist - Revised" (PCL-R: Hare, 1991, 2003) as a measure of the disorder has adequate reliability and validity (Morrissey et al., 2005). The present study aimed to compare the predictive power of the PCL-R in relation to treatment progress with a more general assessment of violence risk, the HCR-20 (Webster, Douglas, Eaves, & Hart, 1997). Method: A sample of 73 residents in a high security intellectual disability service, who had previously been assessed using the PCL-R and the HCR-20, were followed up at 2 years post-assessment, and their outcome determined in terms of two distinct dichotomous variables reflecting definite positive treatment progress and definite negative treatment progress respectively. Results: In line with predictions, the PCL-R Total score and Factor 1 score (Interpersonal and Affective aspects of psychopathy) and the HCR-20 Total score were significantly inversely associated with a positive move from high to medium security hospital conditions within 2 years of assessment. However against prediction, the PCL-R Total score had incremental validity over the HCR-20. The PCL-R Total and Factor 1, but not the HCR-20 Total score, were also significantly associated with negative treatment progress in terms of a move to more restricted treatment conditions. Conclusion: Psychopathy, and in particular its interpersonal and affective manifestations, is a construct which appears to be associated with indirect measures of treatment progress in this high security ID group. However, caution should be applied in the use of a construct with potentially negative connotations in an already devalued population. (Contains 4 tables and 8 notes.)