Emotional blunting can be found after cerebellar lesions. However, the mechanism of such a modification is not clear. We present a patient with emotional flattening and increased risk taking after left cerebellar infarct who had an impaired autonomic reactivity to negative as compared with positive reinforcement. This impairment was demonstrated by the patient's undifferentiated skin conductance responses to negative and positive reinforcement, whereas controls produced larger skin conductance responses after negative feedback. The cooccurrence of emotional flattening and undifferentiated autonomic reactions to positively and negatively valenced stimuli strengthens the role of the cerebellum in the modulation of the autonomic responses.