Autistic adults are at increased risk of both mental and physical health difficulties, and yet can face barriers to accessing healthcare. A meta-ethnographic approach was used to conduct a review of the existing literature regarding autistic adults' experiences of accessing healthcare. Four databases were systematically searched for qualitative and mixed-method studies reporting on the experiences of autistic adults without a co-occurring learning disability accessing adult healthcare services within the United Kingdom. Fifteen studies met the inclusion criteria, and seven steps were used to systematically extract the data and then generate novel themes. Three superordinate themes were identified: "Professionals' lack of knowledge can be damaging," "Need to reduce processing demands" and "Adaptation to improve engagement." This review highlights the wide-reaching damaging impact misdiagnosis, inadequate or inappropriate treatment, overwhelming environments and inaccessible systems can have on the well-being and ability of autistic adults to engage with treatment. The lack of autism knowledge and understanding experienced in interactions with healthcare professionals, along with autistic adult's own communication and sensory processing differences, demonstrates the need for widely delivered training co-produced with autistic adults alongside bespoke and person-centred adaptations.