In this study, we investigated the concurrent and longitudinal relationships between vocabulary and word reading across Spanish and English. One hundred and seventeen 4- to 5-year-old Spanish-English bilingual children attending Head Start programs in the United States were tested for their Spanish and English word reading twice, 5 months apart. We also tested the children's Spanish and English vocabulary and phonological awareness at Time 1. We used multiple regression models to examine the predictive value of vocabulary to word reading cross-linguistically and longitudinally. Results showed that within (Spanish or English) language and concurrent predictions were stronger than cross-language and longitudinal predictions; however, Spanish vocabulary was a significant and unique predictor of English word reading longitudinally. Spanish phonological awareness also played an important role in the relationship between vocabulary and word reading. Our results suggest that helping Spanish-speaking children build their Spanish vocabulary can also improve their English word reading ability.