When bilinguals read in either their first language (L1) or their second language (L2), words from both languages are unconsciously and automatically activated in their mind (e.g., Kroll et al. 2006; Van Heuven and Dijkstra 2002). Many bilinguals, particularly in Florida, choose to learn Portuguese in college as a third language (L3), thus increasing lexical activation of two related languages and potentially complicating lexical retrieval. The present study investigates the effect of learning L3 Portuguese on the typologically similar L2 Spanish. Fifty-four English-Spanish bilinguals and 66 English-Spanish-Portuguese trilinguals completed a lexical decision task in their L2 Spanish. Participants were exposed to real and pseudowords that varied in similarity to words in either Spanish, Portuguese, or unrelated languages. The results indicate that the unintended activation of Portuguese negatively affected the speed at which trilinguals judged words in Spanish, suggesting increased lexical competition. The trilinguals did, however, process the words as correctly as the bilinguals, except when lexical structures were overwhelmingly similar as in the case of Portuguese cognates. The present findings of this study are analyzed in terms of inhibitory control (Green 1998).