Background: The goal of this study was to examine the effect of cognates on Spanish-English bilingual children's English reading fluency. Because cognates lead to higher levels of non-target language activation, we hypothesised that the presence of cognates would result in reduced reading fluency for bilingual children. Methods: Monolingual English-speaking children and Spanish-English bilingual children (ages = 8-13 years) read aloud two stories in English. One story contained cognate words, while the other story did not. Results: Results revealed that bilingual children made more errors and read more slowly when reading a story containing cognates. Conclusions: These findings indicate that the presence of cognates in a text disrupts bilinguals' oral reading fluency, suggesting that lexical-level, local co-activation can have a global effect on bilinguals' ability to engage in a higher-level reading task.