As autism is an invisible and often stigmatised condition, disclosing the diagnosis may lead to both support and/or discrimination. This mixed-methods questionnaire study examined autistic adults' experiences of disclosure in various contexts. The sample consisted of 393 participants aged 17-83 years from two longitudinal surveys. Almost all participants disclosed their diagnosis to someone, most commonly to friends. A significant minority of participants studying and/or working at the time had not disclosed to their education provider/employer. Content analysis of open-ended responses showed participants desired to gain understanding and support from disclosure but feared prejudice. While some received support, others encountered dismissiveness and misunderstanding. Findings highlight the need to improve autism understanding and reduce stigma within and beyond educational and employment contexts.