Background: People with intellectual developmental disorders have significant health disparities and a lack of proper attention to their health needs. They have been underrepresented in scientific research, and very few studies have been carried out using a representative randomized sample. The aim of this study was to describe the methods used in the POMONA-ESP project to recruit a representative and randomized sample of participants with intellectual developmental disorders. Methods: The POMONA-ESP project is an observational cross-sectional study. It aims to explore the health status of people with intellectual developmental disorders across Spain and the use they make of health services. Results and conclusions: The results of the POMONA-ESP project may have a major impact on people with intellectual developmental disorders and society in general. It is the first study to obtain geographically representative epidemiological data from a large sample, information that is fundamental to improving care and healthcare planning for people with intellectual developmental disorders.