In the last 20 years there has been a growing realization that language proficiency consists of much more than grammatical competence (Schmitt & Meara, 1997). In parallel with this realization there has been an increasing awareness that vocabulary knowledge is one of the important components of language knowledge. Development of lexical knowledge is now regarded, by many researchers and teachers, as central to learning a second language. Thus, recent research in the field appears to treat vocabulary as a separate component of language knowledge and consider vocabulary measure as a useful indicator of the proficiency of the learners. One reason of this increased interest in gaining knowledge about learners' vocabulary knowledge results from the desire to develop an assessment tool which is quickly and effectively administered, and which can be used as a placement test. Existing research shows that vocabulary size and overall language proficiency are correlated, and that vocabulary size tests offer a practical placement procedure. However, the vocabulary size tests are decontextualized and hence, it does not give us insight about productive vocabulary knowledge. What is more, for university level students, productive vocabulary knowledge is as crucial as the receptive knowledge. Thus in the present study we investigated the relation between language proficiency levels of foreign language learners and their receptive and controlled productive vocabulary levels. The research design expanded upon earlier methodologies by using equivalent test formats. Receptive knowledge and controlled-productive knowledge were measured using Vocabulary Levels Test (Nation, 1990) and Productive Vocabulary Levels Test (Laufer & Nation, 1999). The study cohorts 40 first-year ELT students in Foreign Languages Education Department at a Turkish state university. © Common Ground, H. Gulru Yuksel, Suzan Kavanoz.