Attention-deficit/hyperactivity disorder (ADHD) is a well-researched condition within multiple editions of the Diagnostic and statistical manual of mental disorders (DSM). Historically, ADHD was believed to be a childhood condition that typically diminished in adolescence. However, current research confirms that not only does ADHD often continue into adulthood, but its impact also has a cumulative effect over the lifespan. Consequently, adults not diagnosed in childhood are a growing demographic of ADHD diagnoses. Within this growing demographic, there is little research on the lived experiences of adults with ADHD, and none were found in Aotearoa New Zealand. The purpose of this study was to explore the similar and differing lived and ableist experiences between groups of adults who were diagnosed with ADHD in childhood, adolescence, adulthood, and those who suspect they have ADHD. Data were collected from eight participants (two from each diagnosis group) using online survey software and online one-to-one interviews. The study used a mixed-method design, and data were interpreted using hermeneutic phenomenology and critical disability theory frameworks to explore participants' lived experiences with ADHD. Findings revealed some differences in life trajectories and between-group experiences of participants with diagnosed or suspected ADHD. However, most experiences revealed a commonality centred around feelings of frustration, rejection, shame, and the lack of personal agency. These experiences and normative social discourses prompted participants to actively police and mask their behaviours and ADHD characteristics. Participants reported lacking crucial knowledge to navigate life internally and externally with ADHD due to the absence of relevant guidance and support. The impact of these internal and external difficulties was compounded by the ableism they faced related to their ADHD. Early ADHD diagnosis followed by comprehensive ADHD information and support within the broader community, i.e. educators and health professionals, would have facilitated more positive lived experiences according to participants. This study indicates that early information, treatment, and support could mitigate the unseen personal toll associated with having ADHD. Additionally, the results highlight the need for further research to understand better the most needed supports and how they might best be made available.