An increasing number of people receive autism diagnoses in adulthood, and there are few studies investigating autistic adults' experiences of disclosing their diagnosis. This study sought to understand autistic adults' experiences of diagnostic disclosure using interpretative phenomenological analysis. Twelve autistic adults, who received their diagnosis in adulthood, participated in one-to-one semi-structured interviews exploring their experiences of diagnostic disclosure. Quality control and reflexivity procedures were used to ensure rigour. Four group experiential themes and nine subthemes emerged: (1) 'Functions of Disclosure' (subthemes: i. Accessing Support; ii. Becoming Myself; iii. Activism and its Burden); (2) 'Approaching the Conversation' (Subthemes: i. Managing Disclosure and Reactions; ii. Disclosure Started Pre-Diagnosis; iii. Impact on Others); (3) 'Negative Effects of Preconceptions' (Subthemes: i. Disbelief and Imposter Syndrome; ii. Not Having My Needs Met; iii. Caution and Avoidance), and (4) 'Acceptance, Openness and Finding Community'. Disclosure served multiple functions for the autistic participants. There was variability in the support that autistic participants received in preparation for disclosing the diagnosis. More consistent post-diagnostic support is required to engage newly diagnosed autistic adults in considering the practicalities and potential consequences of disclosure, its benefits and challenges.