Three experiments used event-related potentials to examine the processing consequences of gender-mismatching pronouns (e.g., “The aunt found out that he had won the lottery”), which have been shown to elicit P600 effects when judged as syntactically anomalous (Osterhout & Mobley, 1995). In each experiment, mismatching pronouns elicited a sustained, frontal negative shift (Nref) compared to matching pronouns: when participants were instructed to posit a new referent for mismatching pronouns (Experiment 1), and without this instruction (Experiments 2 and 3). In Experiments 1 and 2, the observed Nref was robust only in individuals with higher reading span scores. In Experiment 1, participants with lower reading span showed P600 effects instead, consistent with an attempt at coreferential interpretation despite gender mismatch. The results from the experiments combined suggest that, in absence of an acceptability judgment task, people are more likely to interpret mismatching pronouns as referring to an unknown, unheralded antecedent than as a grammatically anomalous anaphor for a given antecedent.