Researchers have called for better support for people with attention deficit hyperactivity disorder (ADHD), after a review found hundreds of thousands could be undiagnosed. Despite recent increases in diagnosis, UK researchers say the number of people with a recorded diagnosis of ADHD is still far below international estimates. The gap was especially large for older adults, with just 0.05 per cent of adults over the age of 65 diagnosed with ADHD, which suggests more than 90 per cent of cases in this age group may be undiagnosed.Greater awareness of ADHD and improved assessments mean it's more often picked up in childhood today. But in past decades, people with ADHD - especially women - were often forced to navigate life without the support a diagnosis can unlock. Rates of new ADHD diagnosis increased significantly after 2020 in most age groups as understanding about the condition became more mainstream - and previous theories that women were not typically affected were disproven. The researchers - from King's College London, University College London and the University of Liverpool - say the findings show recorded diagnosis of ADHD are still unacceptably lower than the best available estimates. 'Our findings highlight that ADHD is likely underdiagnosed across the lifespan,' Dr Gavin Stewart, the study's lead author, said. Older adults with ADHD need more help after years of misdiagnosis, review finds'In recent years, there has been growing awareness of how neurodivergence has been overlooked in middle-aged and older people. 'These ADHD findings mirror what we see in other types of neurodivergence, such as autism, where upwards of 90 per cent of middle-aged and older people are likely to not be formally recognised as being autistic.' He added that a timely diagnosis often acts as a 'gatekeeper' to support - which may be crucial as people age.'The low rates observed in older adults don't necessarily mean that ADHD is uncommon in older age. 'Instead they may reflect historical differences in recognition and access to diagnosis, particularly among generations who grew up before ADHD was widely recognised.' He added: 'The majority of ageing neurodivergent people will not have received a diagnosis and be unsupported, which needs to be urgently addressed.' The study - funded by the Medical Research Foundation and the British Academy - used anonymised data from more than 3.5 million people registered with GP practices in England in 2025 to estimate how many people had a diagnosis at this time. They then compared this with published estimates of ADHD prevalence in the general population, from international studies using data from more than 42 million patients in England to examine trends over a 24-year period.