Aims To develop and validate a self‐report measure designed to assess perceived and experienced stigma for adults with Type 1 diabetes: the Type 1 Diabetes Stigma Assessment Scale (DSAS‐1). Methods A large item‐pool (64 items) was drafted based on qualitative data from interviews with 27 adults with Type 1 diabetes. Eleven adults with Type 1 diabetes completed the draft questionnaire (responding to items using a five‐point Likert scale), and participated in cognitive debriefing interviews. Based on their feedback, the item‐pool was reduced and refined. Adults with Type 1 diabetes (N=898) completed an online survey including the draft stigma questionnaire (41 items) and other validated measures. Psychometric validation included principal components analysis and confirmatory factor analysis (split samples), internal consistency reliability assessment and Spearman's rho correlations. Results Scale reduction techniques resulted in 19 items (α=0.93). An unforced three‐factor solution suggested three subscales: Treated Differently (six items, α=0.89); Blame and Judgement (six items, α=0.88); and Identity Concerns (seven items, α=0.89). This was corroborated with a confirmatory factor analysis, which demonstrated reasonable model fit with the three factors; less so for a single‐factor model. Satisfactory concurrent, convergent and discriminant validity were demonstrated. Conclusions The 19‐item DSAS‐1 is a valid and reliable measure of the perceptions and experiences of Type 1 diabetes stigma. This novel, relatively brief measure has satisfactory psychometric properties. The DSAS‐1 is now available for investigations into the nature and magnitude of the relationships between diabetes stigma and diabetes self‐care behaviours and outcomes. What's new? This paper reports on the rigorous development and validation of the first self‐report measure of perceived and experienced stigma specific to Type 1 diabetes: the novel Type 1 Diabetes Stigma Assessment Scale (DSAS‐1). Questionnaire design was informed by exploratory qualitative research and items were confirmed after cognitive debriefing with people with Type 1 diabetes. Psychometric validation showed that this 19‐item measure was acceptable, had a three‐factor structure, high internal consistency reliability, and satisfactory concurrent, convergent and discriminant validity. The DSAS‐1 could facilitate research to quantify the extent and impact of stigma associated with Type 1 diabetes.