In everyday communication, natural spoken sentences are expressed in a multisensory way through auditory signals and speakers’ visible articulatory gestures. An important issue is to know whether audiovisual speech plays a main role in the linguistic encoding of an utterance until access to meaning. To this end, we conducted an event-related potential experiment during which participants listened passively to spoken sentences and a lexical recognition task. The results revealed that N200 and N400 waves had a greater amplitude after semantically incongruous words than after expected words. This effect of semantic congruency was increased over N200 in the audiovisual trials. Words presented audiovisually also elicited a reduced amplitude of the N400 wave and a facilitated recovery in memory. Our findings shed light on the influence of audiovisual speech on the understanding of natural spoken sentences by acting on the early stages of word recognition in order to access a lexical-semantic network.