‘Early diagnosis’ of Autism Spectrum Conditions (‘ASC’ hereafter) is often promoted as universally beneficial. Despite research identifying the earliest possible reliable diagnoses (at 14-24 months), many are diagnosed later in childhood, adolescence or adulthood. This study aims to: (i) explore the reasons for later diagnoses of ASC; and (ii) understand the impact of this on parents. Narrative methodology (including narrative interviews), afforded the unique benefit of keeping individual, chronological stories intact. This allowed exploration of both explanatory narratives (reasons for later diagnosis) and descriptive narratives (impact of later diagnosis) of two parents of young people who had received a ‘later’ diagnosis of ASC (aged 12 years and 16 years). Findings suggest that later diagnoses were interpreted to have arisen from a complex and highly individualised web of interacting factors. There were considerable differences in parental perceptions of the most beneficial time for the diagnosis, in hindsight. I advocate, therefore, an interactionist conceptualisation of ASC across the lifespan, and suggest that ‘early’ diagnosis is not always possible, necessary or beneficial. I invite further research to build upon these findings, with the ultimate aim of improving experiences and outcomes for children, young people and adults with autism and their families.