Play is often included in autism diagnostic assessments. These tend to focus on 'deficits' and non-autistic interpretation of observable behaviours. In contrast, a neurodiversity-affirmative assessment approach involves centring autistic perspectives and focusing on strengths, differences and needs. Accordingly, this study was designed to focus on autistic perspectives of diagnostic assessments that incorporate play. Autism community stakeholders were consulted on the design of the study. Semi-structured interviews were conducted with 22 autistic adults aged 18-57 years who live in the United Kingdom. Interpretative phenomenological analysis was used to identify themes. Autistic adults highlighted the varying ways in which play was included in their diagnostic assessments, such as via the Autism Diagnostic Observation Schedule. Our findings highlight the importance of better adapting assessment to the heterogeneity of autism. For example, our findings question the extent to which play is useful for assessing autistic women and girls who mask. Our findings also suggest that holistic, neurodiversity-affirmative assessment practices should be adopted. Our findings support the importance of adopting a personalised approach to diagnostic assessments that use play, in addition to assessing strengths and differences as well as needs.