Most of the literature on children with specific language impairment (SLI) is centred on the study of cross-sectional samples and little is known on how language develops in these children--that is, whether it occurs along steps and modes analogous to those observed in normal acquisition, the only difference being significant slowness, or following rather idiosyncratic courses leading to atypical results. This paper presents findings from a longitudinal study of the acquisition of formal aspects of Italian grammar in a child with severe SLI of the so-called phonologic-syntactic subtype or grammatical SLI. The analysis concerns a set of morphosyntactic phenomena sufficiently differentiated in terms of both grammatical properties and modes of acquisition in normal development, so as to offer a panorama that approximates to what can be thought of as an overall morphosyntactic competence: (1) free morphology (prepositions, clitics and articles); (2) bound morphology (verb inflection); (3) WH movement (questions and relative clauses) and (4) the evolution of complex sentences. These phenomena will be dealt with in four independent studies. This paper argues that each domain or even each sub-domain presents its own set of properties, some of which are common to other domains but some of which are not. The results reveal the existence of important dissociations among the various domains and even within specific sub-domains. These dissociations may be ascribed to deficits affecting specific properties of functors or constructions. The picture that emerges is one in which the deficit involves, rather than morphology in the strict sense of a bare set of paradigmatic forms, some properties or components of syntax which are involved in the use, not only of certain morphemes, but of certain extended syntactic constructions as well. This result will be checked against the most widely held current theoretical approaches to SLI.