Résumé : This study undertakes a cross-linguistic comparison of reading and spelling acquisition in French, Portuguese and Spanish languages. It aims to examine several explanatory factors for the well-documented effect of language on the speed of reading and spelling development: differences in orthographic depth and complexity of syllabic structures. A longitudinal study was carried out with first graders in the three languages and with a common assessment procedure. Children were tested in October, February and May on letter knowledge, familiar word and simple pseudoword reading and spelling. Results show that all children were accurate in reading and spelling at the end of the first school year. Differences between languages are highlighted when rate of acquisition and linguistic variables such as lexicality, items length, or complexity of grapheme-phoneme correspondences and of the syllabic structure are considered. These differences will be discussed in the light of the explanatory factors mentioned.