Résumé : This article evaluates the characteristics of the Yes/No test as a measure for receptive vocabulary size in second language (L2). This evaluation was conducted both on theoretical grounds as well as on the basis of a large corpus of data collected with French learners of Dutch. The study focuses on the internal qualities of the format in comparison with other more classical test formats. The central issue of determining a meaningful test score is addressed by providing a theoretical framework distinguishing discrete from continuous models. Correction formulae based on the discrete approach are shown to differ when applied to the Yes/No test in comparison with Multiple Choice (MC) or True/False formats. Correction formulae based on the continuous approach take the response bias into account but certain underlying assumptions need to be validated. It is shown that both correction schemes display several shortcomings and that most of the data relative to the reliability of the Yes/No test presented in the literature are overestimated. Finally, several future research options are proposed in order to attain a straightforward but reliable and valid instrument for measuring receptive vocabulary size. © 2001, Sage Publications. All rights reserved.