Sufficiently developed skills in L1 are considered a precondition for success in the achievement of bilingualism. Moreover, it is reported that language learners whose native language skills are better mastered obtain superior second language proficiency and exhibit higher levels of language competence and accomplishment in L2. This chapter aims at investigating the effect of using test-takers' mother tongue (Turkish as L1) and foreign language (English as L2) in reading comprehension questions in the language classroom. Two groups of adult participants preparing for the Language Exam for Higher Education Institutions (YÖKDIL) were tested under two different conditions. The control group was exposed to the reading test with multiple-choice questions and options in English, while the experimental group was provided with questions and options in their L1. The results indicated that the experimental group participants scored significantly higher than the control group participants, leading to several implications for the use of L1 in language assessment. [This chapter was published in M. Karawiec & J. Kic-Drgas (Eds.), "Foreign language learning and teaching in theory, practice and research" (pp. 135-150). Verlac Dr. Kovac, 2020.]