The aims of the research are to evaluate the factorial validity, internal consistency, measurement invariance, discrimination, and difficulty of the Covid-19 Anxiety Scale (CAS) applied to a sample of Ecuadorian adults (N = 451). The study is based on an instrumental design with Classical Test Theory (CTT) and Item Response Theory (IRT) technics. The results confirmed the validity of the CAS single-factor structure, with measurement invariance across gender and high internal consistency. Additionally, all CAS items displayed adequate discrimination indexes and proper ordering of the difficulty thresholds. In a conclusion, the CAS is a valid measurement scale for Ecuadorian adults.