This study investigates the commonly-held belief in the SLA community that second language acquisition is somehow influenced by the learner’s personality. It builds on previous research on the relation between one personality variable, extraversion, and second language acquisition but is innovative in three ways. First, it examines L2 learners’ speech production in two rather than one L2 and thus puts to the test the hypothesis that the effect of extraversion is stable across different target languages (Dewaele and Furnham 2000). Secondly, whereas most previous studies have investigated the effect of extraversion on fluency (e.g. Rossier 1976, Tapasak, Roodin and Vaught 1978, Busch 1982, Dewaele 1998) this study also looks at the potential effect of this variable on the linguistic accuracy and complexity of learners’ L2 speech production. Thirdly, whereas previous studies were mostly cross-sectional in design, this study adds a longitudinal perspective by considering to what extent the effect of the extraversion–introversion dimension on the fluency, complexity and accuracy of learners’ L2 production remains stable over time. Participants were 25 Dutch-speaking secondary school students learning both English and French as foreign languages in Flanders, Belgium.