Abstract
This article conceptualises a combined autism and ADHD (AuDHD) diagnosis as a residual category not formally represented in diagnostic systems, addressing a critical gap in neurodiversity research. Using Interpretative Phenomenological Analysis of email interviews with six women diagnosed in adulthood, it examines the ambivalence arising from inhabiting this liminal diagnostic space. Residuality generates conflicting feelings about autism, ADHD, and the self, resulting in fragmented identities shaped more by societal narratives than by interpersonal perceptions. Themes include the contradictions between autism and ADHD ('two separate parts of my brain'), their sometimes-complementary relationship ('two sides of the same coin'), and the tension between neurodiversity and medicalisation narratives ('autism is a part of me, ADHD is an add-on'). To resolve this ambivalence, participants sought an objective understanding of their conditions and distinguished between neurodivergent and neurotypical identities. Collectively, their narratives reveal a fluid and dynamic understanding of AuDHD. As the first study to explore the lived experiences of adults diagnosed with both autism and ADHD, it makes an original contribution by developing an AuDHD phenomenology and analytical framework. By amplifying the voices of women historically marginalised, the findings underscore the need for integrated diagnostic processes and tailored support to foster cohesive self-identity. This article contributes to neurodiversity literature, broadens understandings of categorical systems, and illuminates the complexities of navigating residual diagnostic spaces.