Protocol of the Netherlands Autism Register: Methodologies and Data Collection within a Co-Creation Framework

The Netherlands Autism Register (NAR) is a longitudinal, community-based cohort study based on annual data from autistic individuals, their caregivers, and a non-autistic comparison group, covering a broad range of domains including health, education, employment, and well-being. Survey data are supplemented by diverse methodologies including online tests, interviews, ecological momentary assessment, genetic sampling, and neuroimaging.The NAR prioritizes transparent communication, participant reciprocity, and societal impact. Participants receive personalized feedback, and aggregated results are shared through public dashboards and regional policy reports. Autistic individuals are structurally involved at all research stages, within the research team, through advisory panels, and via the NAR Ambassador role.Compared to other international autism cohorts, the NAR is distinctive in its co-creation infrastructure, option for proxy reporting on autistic adults with high support needs, and its integration of diverse methods. The register has generated extensive scientific output and contributed to public debate and evidence-based policy.This protocol outlines the structure, methodology, strengths, and limitations of the NAR, and discusses future directions including reaching underrepresented groups, data harmonisation with other cohorts, and broader societal engagement. The NAR aims to remain a flexible, participant-centred infrastructure supporting autism research and practice in the Netherlands and beyond.