In order to explore the pathophysiological basis of a new rehabilitation therapy in writer's cramp (WC), healthy controls, untreated WC and WC who recovered a legible handwriting after rehabilitation were explored using magnetoencephalography and the somatosensory evoked fields of fingers I, II, III and V in the sensory cortex were studied. In the cortex controlling the dystonic limb, the size of the hand representation in the trained patients was similar to that of healthy controls, and significantly different from that of untrained patients. Trained patients exhibited "super-normal" reorganization of the finger maps. In the cortex controlling the non-dystonic limb, there was little difference between trained and untrained patients and the hand representation was enlarged and disorganized. We hypothesize that prolonged tailored rehabilitation in WC may induce long term plasticity phenomena, lateralized to the cortex controlling the dystonic hand.