Background: Early childhood development is a multifaceted construct encompassing physical, social, emotional and intellectual competencies. The Early Development Instrument (EDI) is a population-level measure of five domains of early childhood development on which extensive psychometric testing has been conducted using traditional methods. This study builds on previous psychometric analysis by providing the first large-scale Rasch analysis of the EDI. The aim of the study was to perform a definitive analysis of the psychometric properties of the EDI domains within the Rasch paradigm. Methods: Data from a large EDI study conducted in a major Irish urban centre were used for the analysis. The unidimensional Rasch model was used to examine whether the EDI scales met the measurement requirement of invariance, allowing responses to be summated across items. Differential item functioning for gender was also analysed. Results: Data were available for 1344 children. All scales apart from the Physical Health and Well-Being scale reliably discriminated between children of different levels of ability. However, all the scales also had some misfitting items and problems with measuring higher levels of ability. Differential item functioning for gender was particularly evident in the emotional maturity scale with almost one-third of items (9 out of 30) on this scale biased in favour of girls. Conclusion: The study points to a number of areas where the EDI could be improved.