Intra-sentential code-mixing presents a number of puzzles for theories of bilingualism. In this paper, we examine the code-mixed English-German utterances of a young English-German-Spanish trilingual child between 1;10 – 3;1, using both an extensive diary kept by the mother and audio recordings. We address the interplay between lexical and syntactic aspects of language use outlined in the usage-based approach (e.g. Tomasello, 2003). The data suggest that partially schematic constructions play an important role in the code-mixing of this child. In addition, we find, first, that the code-mixing was not mainly the result of lexical gaps. Second, there was more mixing of German function words than content words. Third, code-mixed utterances often consisted of the use of a partially schematic construction with the open slot filled by material from the other language. These results raise a number of important issues for all theoretical approaches to code mixing, which we discuss.