The aim of the current study was to investigate expressive affect in children with Williams syndrome (WS) in comparison to typically developing children in an experimental task and in spontaneous speech. Fourteen children with WS, 14 typically developing children matched to the WS group for receptive language (LA) and 15 typically developing children matched to the WS groups for chronological age (CA) were recruited. Affect was investigated using an experimental Output Affect task from the Profiling Elements of Prosodic Systems-Child version (PEPS-C) battery, and by measuring pitch range and vowel durations from a spontaneous speech task. The children were also rated for level of emotional involvement by phonetically naive listeners. The WS group performed similarly to the LA and CA groups on the Output Affect task. With regard to vowel durations, the WS group was no different from the LA group; however both the WS and the LA groups were found to use significantly longer vowels than the CA group. The WS group differed significantly from both control groups on their range of pitch range and was perceived as being significantly more emotionally involved than the two control groups. (Contains 1 table and 4 figures.)