Pronunciation proficiency in the first (L1=Korean) and the second (L2=English) languages of bilinguals who had emigrated to the U.S. was examined. The focus of this presentation is on the effect of age of arrival (AOA) in the U.S. on pronunciation in L1 and in L2. The subject pool consisted of 240 Korean–English bilinguals classified into ten subgroups (ages 2–22) based on AOA. Two groups of monolingual subjects were also tested: 24 Korean and 24 English speakers. The bilingual subjects produced sentences in their L1 and L2 and the monolingual subjects produced sentences in their L1’s. Native listeners from each language group rated the speakers’ pronunciation on a 9‐point scale. The results show a positive correlation between AOA and Korean pronunciation (0.74) and a negative correlation between AOA and English pronunciation (−0.85). In each language group and regardless of AOA, the monolingual subjects were rated better in pronunciation than the bilingual subjects. The implications of these findings to second language acquisition and first language retention will be discussed. © 1997, Acoustical Society of America. All rights reserved.