Abstract This paper presents a case-study of Greek SLI and has the following aims: 1. (i) to present and analyse SLI data concentrating on the use of D-elements in the child's grammatical system: the definite article, object clitics and the wh-phrase what; 2. (ii) to show that there is a clear correlation in the errors involving the morphemes in question and that this is due to a deficit in the determiner system which, in adult form, represents the above morphemes in terms of the same functional category D; 3. (iii) to provide further evidence for the delay in L1 development of object clitics (or agreement) relative to subject agreement (or clitics) showing that a similar pattern is attested in the case of this SLI child. Finally, the analysis presented appears to favour an account of SLI whereby the deficit evidenced by the use of grammatical categories is indeed a grammatical, rather than a processing, deficit and is restricted to the domain of functional categories. The differential success in this child's use of some functional categories (e.g. subject agreement vs. the determiner system) points to the suggestion that SLI involves aspects of the normal route of L1A but also severe delays compared to normal L1A. The question whether the attested delay indicates a selective deficit in the processing strategies and learning mechanisms implemented in SLI cases cannot be unreservedly concluded on the basis of the data from this study only.