Investigations into early vocabulary development, including the timing of the acquisition of nouns, verbs and closed-class words, have produced conflicting results, both within and across languages. Studying vocabulary development in Irish can contribute to this area, as it has potentially informative features such as a VSO word order, and semantically rich prepositions. This study used a parent report adapted for Irish, to measure vocabulary development longitudinally for children aged between 1 ; 04 and 3 ; 04. The findings indicated that the children learned closed-class words at relatively smaller vocabulary sizes compared to children acquiring other languages, and had a strong preference for nouns. (Contains 1 footnote.)