Preliminary results from research show some promising results for the Sex Offender Treatment Services Collaborative – Intellectual Disability (SOTSEC-ID) treatment on offence recidivism. However, further research that explores the processes of behaviour change is required. This study answered the research question: What are the key mechanisms to therapeutic change in individuals with ID who have completed a sex offender treatment programme (SOTP)? A qualitative grounded theory methodology was used to understand the processes of change. A semi-structured interview was used with 12 participants. The results showed that relationship experience, acceptance of responsibility, being able to remember the details of the group, group processes, understanding their own risk and practical strategies were the key areas that are influential in the change process. Barriers to change were also highlighted. The study concluded that there are other factors such as group processes important in the process of change that influence behaviour change, other than the content of the treatment. Group treatment is supported for this population.