The present event-related brain potentials (ERP) study investigated the online integration of morphosyntactic information in auditory French sentences using a violation paradigm. Two main factors were manipulated: (1) The degree of complexity of the morphosyntactic violation, (2) The moment when the agreement violation occurs within the sentence. Both types of morphological agreement violations (intra/inter) elicited a biphasic anterior negativity/P600 ERP pattern. However, the amplitude of this pattern was larger for the interphrasal violation than for the intraphrasal one. This result suggests an easier detection but a more costly integration when the agreement violation occurs between elements belonging to different syntactic units. Moreover, an effect of position was observed but only when the violation concerned elements of a single syntactic unit. Taken together, the present findings suggest that morphological integration may be modulated by both the complexity of morphosyntactic agreement and the moment at which it takes place during the course of sentence processing.