In the wake of the COVID-19 pandemic, a complex phenomenon called the “infodemic” has emerged, compromising coping with the pandemic. This study aims to estimate the prevalence of agreement with misinformation about COVID-19 and to identify associated factors. A web survey was carried out in Portuguese-speaking countries in two stages: 1. the identification of misinformation circulating in the included countries; 2. a multicentric online survey with residents of the included countries. The outcome of the study was agreement or disagreement with misinformation about COVID-19. Multivariate analyzes were conducted using the Poisson regression model with robust variance, a logarithmic link function, and 95% confidence intervals. The prevalence of agreement with misinformation about COVID-19 was 63.9%. The following factors increased the prevalence of this outcome: having a religious affiliation (aPR: 1.454, 95% CI: 1.393–1.517), having restrictions on leisure (aPR: 1.230, 95% CI: 1.127–1.342), practicing social isolation (aPR: 1.073, 95% CI: 1.030–1.118), not avoiding agglomeration (aPR: 1.060, 95% CI: 1.005–1.117), not seeking/receiving news from scientific sources (aPR: 1.153, 95% CI: 1.068–1.245), seeking/receiving news from three or more non-scientific sources (aPR: 1.114, 95% CI: 1.049–1.182), and giving credibility to news carried by people from social networks (aPR: 1.175, 95% CI: 1.104–1.251). There was a high prevalence of agreement with misinformation about COVID-19. The quality, similarity, uniformity, and acceptance of the contents indicate a concentration of themes that reflect “homemade”, simple, and easy methods to avoid infection by SARS-CoV-2, compromising decision-making and ability to cope with the disease.