Although several researchers have already investigated whether knowing more than one language will help students acquire additional languages (Edwards, 1995; Klein, 1995; Cenoz & Genesse, 1998b), one of the still unexplored areas when considering the difference between bilingualism and trilingualism is that of linguistic behaviour referred to adults (Hoffmann, 1999). The present study reflects on the socio-cultural and sociopolitical situation in the Basque Country and its relationship with performance in English as L2 or L3. Thus, a research was carried out by testing matched groups of Monolingual (Ml) (Spanish) versus Bilingual (Bl) (Basque/Spanish) university students, acquiring English for Specific Purposes (ESP) within the following fields: Engineering "mechanical branch", Business Administration, and Nursing. Participants were tested on acquisition of specific technical vocabulary from their fields of study, and they were invited to complete a questionnaire on attitudes towards English. The Bls as a whole outperformed slightly the Mls, suggesting that Bls' immediate/academic aims are somewhat more easily achieved but the differences were not statistically significant. As far as their attitudes towards English are concerned, the differences between Mls and Bls were not significant either, both groups showing overall positive attitudes towards English.