Background: Treatment for adults who set fires relies upon valid and reliable assessment. Research is needed to ensure self-report measures are available for adults with neurodevelopmental disabilities and that they are robust. Method: Qualitative and quantitative data from three rounds of a Delphi exercise with practitioners and a focus group discussion with adults with neurodevelopmental disabilities were used to generate consensus about the accessibility of item adaptations made to the Fire Interest Rating Scale, Fire Attitudes Scale, and the Identification with Fire Questionnaire. Results: Findings suggested the accessibility of current measures could be improved to better meet the needs of adults with neurodevelopmental disabilities and adaptations to all questionnaire items were needed. Conclusion: Following feedback, revisions to current measures were implemented leading to the development of the Adapted Firesetting Assessment Scale with improved accessibility for adults with neurodevelopmental disabilities.