The sensitivity of children's phonological short-term memory performance to languagespecific knowledge was investigated in two experiments. In Experiment 1, monolingual English children, English-French bilingual children, and English children who were learning French as a second language were compared on measures of phonological short-term memory and vocabulary in the two languages. The children's short-term memory performance in each language mirrored their familiarity with English and French, with greater vocabulary knowledge being associated with higher levels of recall of both words and nonwords in that language. This finding was replicated in Experiment 2, in which two groups of children with good knowledge of English and French were examined: native bilingual children who had comparable knowledge of the two languages and non-native bilingual children who had a greater knowledge of their native than second language. The findings indicate that phonological short-term memory is not a language-independent system but, rather, functions in a highly language-specific way.