Sentence comprehension in second language (L2) learners was examined using event-related brain potentials (ERPs). Native Japanese speakers who had learned German as a second language after puberty listened to German sentences which were either correct, semantically incorrect, syntactically incorrect or both semantically and syntactically incorrect. Brain responses were registered while participants listened to these sentences. Grammaticality judgments required after each sentence revealed that their overall performance was not perfect but clearly above chance. When comparing the L2-learners' brain responses to those of native listeners, a variety of differences were observed. Whereas semantically incorrect sentences showed an ERP pattern similar to that of native listeners (a centro-parietal N400-effect), correct sentences elicited a greater positivity in L2-learners than in native listeners, possibly in reflection of greater difficulties in syntactic integration. For sentences containing a phrase structure violation, L2-learners did not show significant modulations of the syntax-related ERP components usually seen in native listeners (i.e. the early anterior negativity and the P600). Furthermore, sentences containing a pure semantic or a combined syntactic and semantic violation elicited a late right anterior-central negativity, an effect which has not been observed for native language processing. The topography of the effect may suggest that these additional processes are based on conceptual-semantic rather than on lexical-semantic aspects.