Does a native language suffer when students take all of their classes in a foreign language, even in their home country? Turkish students studying psychology, economics, or English literature with English as the medium of instruction (N = 91) were explored across a three-year period. Test scores, word fluency measures, and self-ratings were broadly comparable with students enrolled in a standard Turkish curriculum (N = 74). However, differences were attained amid English literature students, many of whom expect careers as English teachers or translators. These students had lower Turkish entrance exam scores, and word fluency scores were higher in English than Turkish, while the reverse was found for all other students, including other English-medium instructed students. The self-assessed L1-Turkish writing abilities of the English literature students also decreased slightly across the three-year study. It is concluded that intense engagement with a foreign language may put the native language at risk for temporary attrition, but studying with a foreign-language as the language of instruction does not.