The PISA assessment framework for mathematics draws heavily on realistic mathematics education - an approach that emphasises the importance of building mathematical models in the context of real-world problems (mathematisation). This approach is strongly endorsed in a few countries (such as The Netherlands), but is less apparent in mathematics curricula elsewhere. While it may present a challenge to some students taking the PISA assessment, it may also offer an opportunity to policy-makers and educators who wish to review their country's mathematics education. Ireland is an example of a country that so far has not espoused realistic mathematics education, and in particular has not emphasised assessment of the process of mathematisation. This paper focuses on the achievements of students in Ireland on PISA mathematics. First, the performance of Irish students in examined in the context of performance in other countries. Then links between the PISA assessment and the syllabus for the Junior Certificate mathematics examination (a state examination taken by all students in Ireland at the end of Grade 9) are considered, and areas of difference are highlighted. The paper concludes by placing the outcomes in the context of other research on mathematics education in Ireland and discussing how the PISA approach and outcomes could influence mathematics education in Ireland in the future.