Infant bilingualism offers a unique opportunity to study the relative effects of language experience and maturation on brain development, with each child serving as his or her own control. Event-related potentials (ERPs) to words were examined in 19- to 22-month-old English-Spanish bilingual toddlers. The children's dominant vs. nondominant languages elicited different patterns of neural activity in the lateral asymmetry of an early positive component (P100), and the latencies and distributions of ERP differences to known vs. unknown words from 200–400 and 400–600 ms. ERP effects also differed for ‘high’ and ‘low’ vocabulary groups based on total conceptual vocabulary scores. The results indicate that the organization of language-relevant brain activity is linked to experience with language rather than brain maturation.