There is a growing trend of adult diagnosis of Autism Spectrum Disorder (ASD). Research has found that diagnosis can prompt a process of sense-making which may be disrupted by lack of post-diagnostic support. Given the continued involvement of many parents in supporting their adult son or daughter with ASD, it is vital to understand their experiences to meet their needs in adapting to the diagnosis. Eleven parents of recently diagnosed adults participated in semi-structured interviews which were analysed thematically. Findings demonstrate that the new knowledge of diagnosis facilitates changes in attributions, interactions and relationships, but can result in unmet emotional and relational support needs. Findings are relevant to those involved in adult diagnosis, and the provision of post-diagnostic support.