Impaired social cognition is a core feature of autism. There is much evidence showing people with autism use a different cognitive style than controls for face-processing. We tested if people with autism would show differential activation of social brain areas during a face-processing task. Thirteen adults with high-functioning autism or Asperger Syndrome (HFA/AS) and 13 matched controls. We used fMRI to investigate 'social brain' activity during perception of fearful faces. We employed stimuli known to reliably activate the amygdala and other social brain areas, and ROI analyses to investigate brain areas responding to facial threat as well as those showing a linear response to varying threat intensities. We predicted: (1) the HFA/AS group would show differential activation (as opposed to merely deficits) of the social brain compared to controls and (2) that social brain areas would respond to varied intensity of fear in the control group, but not the HFA/AS group. Both predictions were confirmed. The controls showed greater activation in the left amygdala and left orbito-frontal cortex, while the HFA/AS group showed greater activation in the anterior cingulate gyrus and superior temporal cortex. The control group also showed varying responses in social brain areas to varying intensities of fearful expression, including differential activations in the left and right amygdala. This response in the social brain was absent in the HFA/AS group. HFA/AS are associated with different patterns of activation of social brain areas during fearful emotion processing, and the absence in the HFA/AS brain of a response to varying emotional intensity.