Researchers have developed several tests of receptive vocabulary knowledge suitable for use with learners of English, but options are few for learners of French. This situation motivated the authors to create a new vocabulary size measure for French, the "Test de la taille du vocabulaire" (TTV). The measure is closely modelled on Nation's (1983) Vocabulary Levels Test (VLT) and follows the guidelines written by Schmitt, Schmitt, and Clapham (2001). Initially, a pilot version was trialled with 63 participants; then an improved version was administered to 175 participants at four proficiency levels. Results attest to the TTV's validity: mean scores across the four frequency sections decreased as the tested words became less frequent, and more proficient learner groups outperformed less proficient groups. The TTV in its current form is intended to be of practical use to teachers and learners, but it is also expected to evolve; ideas for future improvements are discussed.