Recent years have witnessed a significant increase in the interest in international assessments of student performance. In such assessments it is mandatory that all the different-language texts be equivalent to each other, that is, equally difficult to understand. The article summarizes a study made on the topic, examining the problems of equivalence encountered when translating texts in international reading literacy assessments. In the study, three English and Finnish texts used in the PISA 2000 reading test were compared text-analytically. The analysis revealed six different types of problem, which, moreover, differed considerably between the three texts. As a result of the problems, none of the three text pairs were fully equivalent in difficulty. The study suggests that it will probably never be possible to attain full equivalence of difficulty in international reading literacy studies; however, by developing the translation work, a relatively high level of equivalence (and validity) seems attainable. (Contains 2 tables and 2 footnotes.)