Purpose: Stigma cultures in healthcare settings are the organizational-level norms values, assumptions, physical façades, and practices that govern day to day activities and interactions. Aspects include poor quality of care, coercive care, a punitive and patronizing atmosphere, and disempowerment to make treatment decisions. To evaluate the effectiveness of interventions to reduce stigma cultures in healthcare settings, valid and reliable measures are needed. This paper describes the development and preliminary testing of a measure to assess mental illness related stigma in healthcare cultures from the perspectives of service users., Methods: Item generation was grounded in the lived experiences of people with a mental or substance use disorder (n = 20) reflecting their personal experiences with physical or mental healthcare encounters. Wherever possible, items were adapted from existing scales. Items were rated on a 4-point agreement scale with higher scores indicating higher stigma. Following the qualitative analysis, survey data (n = 2,476) were collected and exploratory and confirmatory factor analysis on split halves of the sample were conducted., Results: The analyses provided statistical support for a 23-item unidimensional scale that could be used in any healthcare setting to assess key aspects of stigma cultures such as poor quality of care or lack of person-centered care. Reliability was high (0.92) and aggregated scale scores (ranging from 0 to 92) were approximately normal., Conclusions: Though further testing is needed, the resulting Stigma Cultures in Healthcare scale is intended to be used across a range of physical and mental healthcare settings to assess the extent to which key aspects of care are experienced as stigmatizing by clients with mental or substance use disorders., Competing Interests: Declarations. Ethical approval: All procedures and analyses described in this paper were approved by the Queen’s University and Affiliated Teaching Hospitals Research Ethics Board. Competing interests: Both authors have received consultation fees from The Mental HealthCommission of Canada for their subject matter expertise in stigma, stigma reduction, and measurement development., (© 2024. The Author(s).)