Language disorders, and Specific Language Impairment (SLI), have been extensively studied in a number of different, though thus far almost exclusively Indoeuropean, languages. For other languages such as Turkish, Vietnamese, or Arabic, however, findings on the outcome of SLI are rare. In this context, the growing number of migrant children in European countries with a variety of first languages can be seen as a challenge to linguistics and to language assessment: The lack of empirical findings on SLI in these languages brings up the question of how the impairment is manifested in bilingual children with a migrant background. In order for a language disorder to correctly be labelled SLI, it needs to be identified in both languages. This paper presents findings from a study examining the grammatical features of Turkish first language acquisition in Germany, while focusing on Turkish case morphology. For this purpose, it compares the data of three typically-developing children and two children with deviant language development. Moreover, it presents a first interpretation of the outcome of grammatical SLI in bilingual Turkish children and discusses suggestions for diagnostic assessment procedures. (Contains 9 notes, 4 tables, and 1 figure.)