We report an event-related brain potential (ERP) study examining how readers process sentences containing anaphoric reference to quantified antecedents. Previous studies indicate that positive (e.g. many) and negative (e.g. not many) quantifiers cause readers to focus on different sets of entities. For example in Many of the fans attended the game, focus is on the fans who attended (the reference set), and subsequent pronominal reference to this set, as in, Their presence was a boost to the team, is facilitated. In contrast, if many is replaced by not many, focus shifts to the fans who did not attend (the complement set), and reference to this set, as in. Their absence was disappointing, is preferred. In the current studies, the electroencephalogram (EEG) was recorded while participants read positive or negative quantified statements followed by anaphoric reference to the reference set or complement set. Results showed that the pronoun their elicited a larger N400 following negative than positive quantifiers. There was also a larger N400 on the disambiguating word (presence/absence) for complement set reference following a positive quantifier, and for reference set reference following a negative quantifier. Findings are discussed in relation to theoretical accounts of complement anaphora.