Researchers have recently introduced various LexTALE-type word recognition tests in order to assess vocabulary size in a second language (L2) mastered by participants. These tests correlate well with other measures of language proficiency in unbalanced bilinguals whose second language ability is well below the level of their native language. In the present study, we investigated whether LexTALE-type tests also discriminate at the high end of the proficiency range. In several regions of Spain, people speak both the regional language (e.g., Catalan or Basque) and Spanish to very high degrees. Still, because of their living circumstances, some consider themselves as either Spanish-dominant or regionallanguage dominant. We showed that these two groups perform differently on the recently published Spanish Lextale-Esp: The Spanish-dominant group had significantly higher scores than the Catalan-dominant group. We also showed that the noncognate words of the test have the highest discrimination power. This indicates that the existing Lextale-Esp can be used to estimate proficiency differences in highly proficient bilinguals with Spanish as an L2, and that a more sensitive test could be built by replacing the cognates.Keywords LEXTALE_Esp . Vocabulary size . Language proficiency . Bilingualism Proficiency has a central role in research on bilingualism (Lemhöfer & Broersma, 2012). Indeed, the second language (L2) proficiency has been demonstrated to affect performance in a variety of experimental tasks and paradigms. Davis et al. (2010), for instance, observed that highly proficient bilinguals show an interlingual cognate priming effect of the same magnitude as a within-language repetition effect (e.g., for an English-Spanish bilingual, there is as much priming for the prime-target pair rico-RICH as for the pair rich-RICH). The same was not true for beginning bilinguals, when the prime was in L2 and the target in the first language (L1). Rossi, Gugler, Friederici, and Hahne (2006) reported that highly proficient late L2 learners showed the same event-related potential responses to syntactic violations in sentences as L1 speakers, but this was not true for low-proficiency L2 learners, who had a qualitatively different response to the violations. Other neuroscientific research has indicated that the pattern of brain activation is modulated by L2 proficiency. Whereas highly proficient L2 speakers activate the same brain areas as L1 speakers during lexico-semantic processing in the L2, less proficient bilinguals show the engagement of additional brain areas when performing tasks in the L2 (see Abutalebi, 2008, and