Studies on the acquisition of a third language (L3) in a bilingual context have shown thatliteracy in two languages facilitates the acquisition of a third (Cenoz & Valencia, 1994;Swain, Lapkin, Rowen, & Hart, 1990). The present study seeks to contribute to this line ofresearch by comparing the acquisition of English as an L3 by Catalan/Spanish bilingual highschool students in an immersion program with the acquisition of English by Spanishmonolinguals. Data from 201 participants were submitted to a hierarchical multiple regressionanalysis, rendering results that show that bilingualism indeed has a positive effect on theacquisition of an L3. The evidence is discussed from a cognitive perspective.