Background: This report describes a cognitive behavioural group intervention for women with mild and borderline intellectual disabilities detained in a secure hospital setting because of their fire-setting behaviour. The study aimed to examine participants' motivations for setting fires, their responses to an intervention designed specifically for this group and to monitor their progress over an extended follow-up period. Methods: A number of fire-specific and clinical assessments were administered before the intervention started and immediately after it concluded to examine trends in the group data. Detailed case study material was collected in order to describe participants' engagement in and reactions to the treatment process, and their status at 2-year follow-up. Results: The intervention successfully engaged participants in the therapy process, all of whom completed the programme. Scores on measures related to fire-related treatment targets and clinical measures pertinent to motivations for fire-setting generally improved following the intervention. There were no reports of participants setting any fires 2 years after the intervention programme was completed. Conclusions: The group intervention appeared to be acceptable and beneficial to study participants. This pilot study needs to be extended into a more robust evaluation of this approach with this group.