Research and evaluation focused on students’ attitudes towards science and mathematics require the availability of culturally appropriate instruments in the language of the studied population. We present the translation and adaptation of the Mathematics and Science Attitude Inventory for its use with Puerto Rican Spanish-speaking secondary school students, within the evaluation of a teacher professional development project. We used a cross-cultural translation and adaptation model that frames these processes in the context of establishing validity and reliability of a measure by assessing the equivalence of the original version and the translated one in various dimensions: semantic, content, technical, criterion, and conceptual. Results obtained provide evidence of the equivalence between the English and Spanish versions of the inventory, as well as the reliability and validity of both versions for our context. The feasibility and utility of the cross-cultural model used were also demonstrated. This model is a valuable guide for the translation and cultural adaption of research and evaluation instruments in diverse languages and cultures.