Much comparative research into education-related beliefs has exploited questionnaires developed in one culture for use in another. This has been particularly the case in mathematics education, the focus of this paper. In so doing, researchers have tended to assume that translation alone is sufficient to warrant a reliable and valid instrument for cross-cultural research, prompting concerns that a number of necessary equivalences are unlikely to have been addressed. In this paper, we consider the nature of these equivalences before examining the literature of a different field, healthcare research, to synthesise an approach to instrument adaptation that is pragmatic but rigorous. Finally, we demonstrate how this pragmatic approach, incorporating extensive cognitive interviews, enabled us to adapt and refine a mathematics-related beliefs questionnaire, developed in Flanders, for use with students aged 14-15 in England and Spain. Analyses indicate that the instrument so developed is multidimensional, reliable and cross-culturally valid. Some implications are discussed.