This study aimed to investigate the extension of bilingual advantage into trilingualism and the role of proficiency in possible cognitive effects of third language (L3) experience.To this end, the data were collected from 51 Turkish young adults in three language groups through the administration of the Stroop task.The first group had 17 high-school graduates learning English and Arabic at intermediate-level.The second group consisted of 17 junior students studying Islamic Studies offering instruction in Turkish (30%), English (40%) and Arabic (30%).The last group had 17 junior students from English medium Social Sciences programs.Results revealed no additional cognitive benefits of trilingualism compared to bilingualism, yet high proficiency in L3 was associated with the enhancement of inhibition.