Abstract. While previous research discussed populism as a phenomenon of declining trust, we investigated the predictive value of populist attitudes for citizens’ trust, attitudes, and behaviors during the COVID-19 pandemic. Moreover, we tested the role of trust in several institutions simultaneously. As preregistered, the cross-sectional ( N = 1,090) and longitudinal ( n = 216) data collected (April to June, 2020) in Germany ( n = 617) and Poland ( n = 473) showed that stronger populist attitudes predicted higher trust in (a) alternative news media but less trust in (b) mainstream news media, (c) political institutions, and (d) scientific institutions. Moreover, we found negative effects of populist attitudes on acceptance and compliance, mediated via trust in political and scientific institutions (but not news media).