An important, but unexamined, predictor of mental illness stigma is an extrinsic religious orientation, or a motivation to participate in religion for social reasons. High extrinsic religious orientation correlates positively with other types of prejudice. The purpose of this study was to examine the relationships between diagnosis, religious orientation, and stigma. Participants (n = 334) were recruited via Amazon Mechanical Turk, randomized to read one of three vignettes about a person with a mental illness (schizophrenia, anorexia nervosa, or depression), and completed measures of mental illness stigma and religious orientation. Using multiple regression analyses, researchers assessed the impact of diagnosis, extrinsic-personal, extrinsic-social, and intrinsic religiosity on specific aspects of stigma as measured by the Attribution Questionnare-27 subscales (i.e., blame, anger, pity, danger, fear, help, avoidance, segregation, and coercion). Analyses suggested that diagnosis was a key predictor of stigma, and that schizophrenia was the most stigmatized. Multiple regression analyses revealed that extrinsic religiosity was also an important predictor of stigma; extrinsic religiosity was associated with increased stigma in several domains and moderated the relationship between diagnosis and overall stigma. High extrinsic religiosity was associated with increased stigma, with both simple and moderating effects. Simple effects may be related to increased social conformity among religious people. As a moderator, extrinsic religiosity may weaken the link between diagnosis and stigma; high extrinsic religiosity was associated with greater stigma for diagnoses perceived as more “controllable” (i.e., anorexia nervosa, depression) such that levels were similar to schizophrenia.