The present study uses event-related potentials (ERPs) to examine how native Spanish speakers comprehend overt pronouns in two referentially challenging contexts: Sentences in which a pronoun has two gender-matching antecedents (referential ambiguity), and sentences in which there are no gender-matching antecedents (referential failure). Participants read these sentences for comprehension while their brain activity was recorded. Results revealed a sustained positivity for referentially ambiguous pronouns, in contrast to a sustained negativity observed in previous studies of English and Dutch, and a positivity (P600) for referential failure, in line with previous studies. There was no relationship between ERPs and working memory measures. These results suggest that speakers of different languages may differ in how they process referential ambiguity, but not referential failure.