Purpose: The current study investigates the predictive value of neurobiological factors in relation to detainees' treatment outcome, in order to better understand why some individuals respond favorably to treatment while others do not. It was hypothesized that low levels of heart rate activity are associated with poor treatment outcome and that weak neurocognitive functioning is predictive of more benefit from therapy. Methods: Background characteristics, behavioral measures, neurocognitive functioning and heart rate activity of 121 male detainees selected for cognitive skills training were assessed. Outcome measures included program completion, evaluations by trainers and ward staff, and detainees' self-reported motivation and treatment evaluation. Results: Concentration performance, a neurocognitive skill, significantly predicted treatment dropout over and above background and behavioral measures, including self-reported motivation. In addition, high selfreported 'meanness', a psychopathic feature, was associated with low treatment motivation and an expectation bias seemed to be present among highly motivated detainees. These results did not confirm the hypotheses. Conclusions: Offenders who are characterized by a decreased concentration performance, low motivation and increased meanness, are less likely to benefit from treatment. The results have the potential to improve the current treatment assessment procedures in order to reduce dropout rates and, eventually, recidivism rates.