In two experiments, we investigated the morphosyntactic decomposition and semantic composition of acoustically presented German compound words. A left-anterior negativity (LAN) was found in the ERP for gender incongruent, initial compound constituents although these constituents are syntactically irrelevant in German. This LAN provides online evidence for morphosyntactic decomposition. Experiment 1 showed also preliminary evidence for semantic composition, which was further investigated in Experiment 2 by comparing semantically transparent and opaque compounds. Transparent compounds elicited an increased negativity with a centroparietal maximum that occurred during the presentation of the head constituent. This negativity is suggested to reflect the semantic integration of compound constituents that is necessary after the constituents have been accessed separately.