Individuals with Williams syndrome (WS) are well known for their friendly behaviour and tendency to approach strangers indiscriminately as if everybody were their friend. This tendency to approach strangers is mirrored in their ratings of unfamiliar face stimuli. Here we examined their perception of unfamiliar expressive faces and found that individuals with WS do not always see faces as being highly approachable. Happy faces were rated as more approachable by individuals with WS than by controls. In contrast, the other less approachable face stimuli were rated lower on approachability by individuals with WS than by controls. Thus, it appears that although individuals with WS will discriminate people in terms of approachability, they have difficulty inhibiting their strong compulsion towards social interaction. The form of this strong pro-social compulsion is discussed both in terms of friendliness and in terms of the heightened salience of social stimuli (social stimulus attraction).