To date, research on bilingual first language acquisition has tended to focus on the development of higher levels of language, with relatively few analyses of the acoustic characteristics of bilingual infants’ and childrens’ speech. Since monolingual infants begin to show perceptual divisions of vowel space that resemble adult native speakers divisions by about 6 months of age [Kuhl et al., Science 255, 606–608 (1992)], bilingual childrens’ vowel production may provide evidence of their awareness of language differences relatively early during language development. This paper will examine the development of vowel categories in a child whose mother is a native speaker of Castilian Spanish, and whose father is a native speaker of American English. Each parent speaks to the child only in her/his native language. For this study, recordings made at the ages of 2;5 and 2;10 were analyzed and F1−F2 measurements were made of vowels from the stressed syllables of content words. The development of vowel space is compared across ages within each language, and across languages at each age. In addition, the child’s productions are compared with the mother’s and father’s vocalic productions, which provide the predominant input in Spanish and English respectively.