Lived Experience, Family, and Clinician Perspectives on Barriers to Adult Autism Diagnosis and Post-Diagnostic Supports: A Mixed-Methods Systematic Review.

UNLABELLED: Obtaining a late Autism diagnosis and post-diagnostic supports can be a long, complicated process. Prior research has explored the perspectives of those with lived experience, family members, and clinicians, but has not yet provided a comparison of their perspectives. This review integrates qualitative and quantitative literature on barriers to diagnosis and post-diagnostic supports from these three perspectives. We also examine barriers reported by gender-diverse and ethnic minority Autistic people. We searched Web of Science, PsycINFO, Embase, Medline, and ProQuest Dissertations & Theses. Study quality was evaluated using Joanna Briggs tools and the Delphi Critical Appraisal Tool. We followed mixed-methods integrative methodology and thematic synthesis approaches to synthesise findings, and GRADE-CERQual to assess confidence in the evidence generated. We included 50 studies on 4487 adult-diagnosed participants, 902 self-identifying participants, 217 family members, and 198 clinicians. Ethnicity and gender identity were scarcely reported. Three analytical themes emerged: recognition and decision-making; negotiation at the interface; and resistance and resolutions. Tensions between stakeholders were seen in several areas, including conflicting views on access to information, diagnostic tools, self-identification, and challenges posed by co-occurring mental health conditions. The GRADE-CERQual appraisal showed moderate-to-high confidence in the findings. Barriers were compounded for gender-diverse and ethnic minority participants. Differences in how barriers (e.g., perceptions of diagnostic practices) are interpreted by stakeholders may themselves hinder access to services. We outline research and clinical implications, including transparent demographic reporting and improved access to information about services. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at https://doi.org/10.1007/s10882-026-10055-x.