--- - |2 Abstract Racial, ethnic, religious, and sexual minority populations are growing rapidly in the West. We investigate predictors and consequences of threat responses to perceived minority group size, and perceptions of minority group size itself. Study 1 (N = 274) finds that right‐wing adherence predicts greater size threat, whereas lower numerical ability predicts larger perceived group size (confirmed in Studies 2–3). Study 2 (Sample 1, N = 124; Sample 2, N = 263) finds that the relation between right‐wing adherence and prejudice toward minorities exhibits an indirect effect via group size threat (but not perceived size), explaining 35–66% of this relation. Study 3 (N = 310) finds a comparable indirect effect explaining 27–40% of this relation, even after statistically controlling for indirect effects of realistic, symbolic, and terroristic threat. These findings provide novel insights into psychological processes surrounding perceived minority group size, identifying size threat as especially crucial in understanding intergroup relations. - European Journal of Social Psychology, EarlyView.