It has been claimed that Williams syndrome (WS) children have an unusual command of language reminiscent of "cocktail party speech." An analysis of the spoken language of 43 school-age WS children showed a subgroup (37% of the sample) who produced significantly more speech, more complex utterances, more social phrases and clichés, and more complex communicative functions, when compared with the rest of the WS group. Thus, hyperverbal speech is not a consistent manifestation of the syndrome. The speech of 20 WS children was compared with the speech of mentally handicapped control children. There were no differences in the quantity of language produced, in its grammatical complexity, or in the range and frequency of communicative functions that were expressed. But more of the WS children had an over-familiar manner and used more adult vocabulary and social phrases. It is suggested that their speech appears so different from the speech of other mentally handicapped children primarily because of these vocabulary and stylistic differences, and because of the contrast between their verbal abilities and their more impaired visuo-spatial and motor skills.