Background: Peru is the worst affected country by the COVID-19 pandemic showing the world highest mortality rate, thus triggering an increased mental health burden. Nevertheless, there are few population-based epidemiologic surveys of mental disorders in Peru; Therefore, nationally representative research is needed to understand the underlying population-based mental health burden and identify unmet care needs. Objective: The present study aims to estimate the prevalence and patterns of psychiatric disorders, mental health service use, and unmet mental health care needs Methods: This cross-sectional study will collect information from a multistage random sample of 19,500 households. A child, an adolescent, an adult, and an older adult will be interviewed in the household. Trained staff will conduct face-to-face diagnostic interviews via the Preschool Age Psychiatric Assessment, the Child and Adolescent Psychiatric Assessment, the WHO's Composite International Diagnostic Interview, and the Alzheimer Disease 8 Scale. In addition, descriptive and inferential analysis for complex sampling will be performed to estimate the prevalence and correlates. Ethics and dissemination: IRB will approve the research protocol before the commencement of the study. Only respondents who signed their informed consents or assents will participate in the study; The parent or guardian will sign the consent for the participation of preschool children. The research findings will be disseminated in peer-reviewed publications, scientific reports, and presentations at national, and international meetings. In addition, de-identified data and study results will be posted on the Peruvian National Institute of Mental Health (PNIMH) website to be freely available to policymakers, researchers, and the general public.