This study sought to contribute to the growing literature on third and subsequent language learning by establishing whether bilingualism has an effect on ability to learn a subsequent language, as indicated by a measure of language aptitude, the Defense Language Aptitude Battery (DLAB). Test results were obtained for 142 diplomatic officers in the Australian Department of Foreign Affairs and Trade (DFAT). The officers' language biographies were elicited using an online questionnaire and were used to classify them as monolingual or bilingual, and with or without experience of formal language training. Results showed that bilinguals performed better on the aptitude test than monolinguals, as did those with prior formal training. This suggests that bilinguals' metalinguistic awareness, and likelihood of success in subsequent language learning, is higher than that of monolinguals, at least as measured by the DLAB.