This article sets itself two main aims. The first is to describe the rationale behind the decision to adapt for Polish learners the Modern Language Aptitude Test (MLAT) by Carroll and Sapon (1959), rather than to develop a new measure. The reasons behind the decision are discussed in the context of the relevant individual differences (ID) research in Poland and the need for a reli- able and theoretically valid measure of foreign language (FL) aptitude for L1 Polish is articu- lated. The other aim is to describe the development, piloting and initial validation of the Polish MLAT-based adaptation of a new measure of FL aptitude. Two methods of test adaptation (trans- lation and paraphrase) are discussed and justified with relation to the cur...