No tools quantify the experience, psychological, and practical impact of receiving a diagnosis from a non-deficit perspective. Autism is increasingly late diagnosed in adulthood. The Impact of Diagnosis Scale (IODS) was initially developed for borderline personality disorder. We aimed to develop a revised version suitable for autistic adults and potentially other diagnostic groups. Following a trial of a preliminary revision, the researchers and autistic research advisors co-produced an expanded pool of 46 items, scored on 7-point Likert-type scale, within 6 hypothesized domains. Scale reduction processes were applied to data from 125 formally diagnosed autistic adults. Following iterative rounds of factor analysis using maximum likelihood estimation with Promax rotation, 22 items were retained across 4 domains to comprise the IODS-R. The IODS-R adds new understanding to the experience of receiving an autism diagnosis in adulthood. It may be useful for evaluating diagnostic services and other diagnostic groups.