This article examines the Irish results in PISA (Programme for International Student Assessment) mathematics, with particular reference to gender differences. As in most PISA countries, male students in Ireland achieved a significantly higher mean score than females on the overall mathematics scale in all PISA cycles to date. In 2003, when mathematics was a major assessment domain, male students in Ireland outperformed females on all four mathematics subscales representing the overarching ideas, with the largest difference on Space and Shape. This is contrasted with the stronger performance of female students on the state Junior Certificate (JC) mathematics examination, taken by all students at the end of 9th Grade. The authors' analyses suggest that the stronger performance of male students on PISA is related to differential performance across content areas and cognitive levels, stronger performance at the top end of the overall mathematics proficiency scale, stronger performance on multiple-choice items, and stronger self-efficacy in and lower anxiety about mathematics. The findings are discussed in relation to existing theories of gender differences in mathematics and to features of schooling in Ireland. Throughout the article, reference is made to gender difference in PISA mathematics in other European countries.