In a second language acquisition, the lexical interferences of L1 on L2 occur very frequently. In this paper, it is argued that the study of lexical interferences can be used to observe the acquisition level of grammatical structures. The following analysis takes into consideration the written works of twenty-two university students, beginners in the study of German language as a foreign language. The author studies the frequency of Italian words occurrence in the twenty-two written works and tries to classify the occurrence contexts. The frequency of Italian words is very high in concomitance with some characteristic grammatical German structures such as the Nominalklammer and the Verbalklammer, which have a different word order if compared with the correspondent Italian structures. Even if the use of Italian words demonstrates an interference process of L1 on L2, however, the word position proves in some cases that the students acquired the grammatical structures of the target language.