Support staff working with individuals with intellectual disability (ID) and challenging behaviour experience high levels of work-related stress. Preliminary theoretical and experimental research has highlighted the potential suitability of acceptance and mindfulness approaches for addressing support staff stress. This study examines the effectiveness of an acceptance and mindfulness-based stress management workshop on the levels of psychological distress and well-being of support staff working with individuals with ID and challenging behaviour. Support staff (n=120) were randomly assigned to a workshop intervention condition (n=66) or to a waiting list control condition (n=54). Measurements were completed at three time points (pre-, post and 6 week follow-up) for: psychological distress, well-being, perceived work stressors, thought suppression, and emotional avoidance/psychological inflexibility. Main Findings: The intervention led to significantly greater reductions in distress in the intervention group than in the control group. This was largely maintained at 6 week follow-up. This effect was more pronounced amongst a subsample that had shown higher levels of psychological distress at baseline. Thought suppression was found to reduce significantly in the intervention group between post intervention and follow-up, although no significant change was found in well-being or experiential avoidance/psychological inflexibility. Overall, results demonstrated support for the effectiveness of an acceptance and mindfulness-based intervention in reducing distress.