Abstract
Grammatical performance of individuals with Williams syndrome (WS) has been reported as being unimpaired, despite their comparatively low IQ and poor general cognitive ability. Specific language impairment (SLI) is often seen as the converse of WS, showing poor linguistic ability relative to level of cognitive functioning. Detailed profiles of language functioning in four children with WS and four with SLI are presented which show a much less clear-cut picture than is often portrayed and suggest that children with WS may be less linguistically able than is commonly reported. A comparison of results on standardised tests with performance in real conversations shows that not only the children with SLI but also those with WS have significant linguistic difficulties. This has clear implications for their management by speech and language therapists.