Turkey has hosted many international students from various countries in recent years. After learning Turkish in Turkish language teaching centers of the universities, these students move onto their undergraduate or graduate studies at different departments where they are required to use Turkish in all academic skills without reservation. The aim of this study was to investigate academic Turkish problems of international students. The subjects of the study were 697 international students from 54 universities, and 203 content-area instructors from 15 different universities in Turkey. The quantitative data were gathered through questionnaires and analyzed using Statistical Package for the Social Sciences program and the qualitative data were gathered through semi-structured interviews and analyzed using descriptive analyses. The study revealed that insufficient vocabulary range is the primary source of difficulties international students encounter during the instruction of their content courses. Moreover, instructors are of the opinion that students have much more difficulties in using academic Turkish than they themselves perceive. It is hoped that the results of the present study will contribute to the development of curriculum and materials in such a way as to use it for the benefit of international students pursuing their studies at Turkish universities.