INTRODUCTION: Inclusion of older adults in research ensures both equity and relevance. We used National Institute of Health and Care Research Year of Birth data to describe inclusion of older adults in contemporary UK clinical research. METHODS: We worked with English research networks to collect individual participant level data on recruits into National Institute of Health and Care Research portfolio studies. We used data from 2022-2023 to 2023-2024 to assess participation. We described data in terms of geography, primary speciality managing the study and study characteristics. In subgroup analyses, we assessed inclusion of the 'oldest old' (aged over 85 years) and inclusion in research from three exemplars: heart failure, Parkinson's disease and palliative care. RESULTS: In total, 455 734 participants were included in the analyses. The most common age group included in UK research was 65-74 years (15.5%). People aged over 85 years were 3.2% of all recruits, and this proportion decreased over time. There was modest geographical variation in participant age but marked variation by recruiting speciality. People aged over 85 years accounted for less than 5% of the total participants recruited in 9 of 14 specialities assessed. Older adults were less likely to be recruited into commercial studies. For three conditions of interest, recruitment did not match population epidemiology. CONCLUSION: This project has demonstrated feasibility of collecting participant age data at scale and provides important metrics for understanding study participation. While there is scope to improve older adult participation across all the study portfolio, there are major equity issues around inclusion in certain speciality areas and commercial research. To complement this abstract, a video abstract is available online.