Purpose <p>Whether autism is increasing is a subject of growing interest to researchers, health and social care professionals, policymakers, and the general public. We examined trends over time in the proportion of adults in England self-reporting as autistic, utilising data from an annual repeated cross-sectional survey series of adults registered with a General Practice in England.</p> Methods <p>We report annual unweighted frequencies and weighted percentages (with 95% confidence intervals) for survey respondents self-reporting autism for 2018 to 2025, with equivalent data for self-reporting learning disability and a mental health condition. We additionally report the percentage change for 2019 to 2025, compared to a 2018 survey year baseline. Disaggregated data was reported according to age group, gender identity, and ethnicity.</p> Results <p>The weighted percentage of adults self-reporting as autistic has increased from 0.9% (95% CI 0.9–0.9) in 2018 to 2.6% (95% CI 2.5–2.7) in 2025, representing a 188.9% increase over a 7-year period. More modest percentage increases over this same time period were observed for learning disability (26.7%) and mental health condition (51.6%). The majority of the increase in adults self-reporting as autistic took place between the 2021 and 2025 survey years, over which time there was a 136.4% increase.</p> Conclusion <p>There has been a substantial increase in adults self-reporting as autistic in England over a relatively short period of time, with an absence of similar increases in self-reporting as having a learning disability or a mental health condition. Further research is required to better understand the factors underpinning this change.</p>