The study of inter-individual differences at behavioural and neural levels represents a new avenue for neuroscience. The response to socio-emotional stimuli varies greatly across individuals. For example, identification with the feelings of a movie character may be total for some people or virtually absent for others. Inter-individual differences may reflect both the on-line effect (state) of the observed stimuli and more stable personal characteristics (trait). Here we show that somatomotor mirror responses when viewing others' pain are modulated by both state- and trait-differences in empathy. We recorded motor-evoked potentials (MEPs) induced by Transcranial Magnetic Stimulation (TMS) in healthy individuals observing needles penetrating a model's hand. We found a reduction of corticospinal excitability that was specific for the muscle that subjects observed being penetrated. This inhibition correlated with sensory qualities of the pain ascribed to the model. Moreover, it was greater in subjects with high trait-cognitive empathy and lower in subjects with high trait-personal distress and in those with high aversion for the observed movies. Results indicate that somatomotor responses to others' pain are influenced by specific onlookers' personality traits and self-oriented emotional reactions. Our findings suggest that multiple distinct mechanisms shape mirror mapping of others' pain.