This study investigated whether children with Specific Language Impairment (SLI) show difficulty acquiring Noun Phrase structure. A group of 10 children with SLI with an average age of 5 was tested with 3 experiments designed to probe their comprehension of articles, simple and complex possessive phrases, and their adherence to syntactic principles of binding and “wh” extraction. Their performance was compared with 2 groups of normally developing children, one group of 10 younger children matched to the SLI group according to Mean Length of Utterance (LM or Language Match group), and one group of 10 children matched to the SLI group according to age (AM or Age Match group). A spontaneous language sample was also obtained from the SLI and LM groups to compare their performances on spontaneous language and comprehension tasks. Significant differences were found between the SLI and AM groups in all tasks subject to statistical testing, and between the SLI and LM groups in some of the tasks. In tasks where significant differences were not found, there were differences in the response patterns of the SLI and LM groups. These results suggest that children with SLI show marked difficulty with Nominal Phrases and that their difficulty can be described as a limitation in their ability to project fully hierarchical phrase structures that affect their verbal and nominal system similarly. Comparisons between performance on spontaneous language and comprehension tasks suggest that reliance on spontaneous language production only can lead to an overestimation of children's grammatical ability.