Congenital mirror movements. Abnormal organization of motor pathways in two patients. We studied 2 patients with congenital mirror movements by means of various neurophysiological and metabolic techniques, including mapping of motor evoked potentials to transcranial electrical and magnetic stimulation, premovement and somatosensory evoked potentials, kinematics of voluntary movements, muscle reflexes, and positron emission tomography (PET). Abnormalities in maps of motor and premovement potentials and in PET scans were consistent with a bilateral representation of hand muscles in the motor cortex, the existence of physiologically active connections capable of conducting fast efferent volleys from the motor cortex to ipsilateral muscles, the presence of mirror EMG activity in either hand with intended voluntary movement of the other hand, the absence of mirrored EMG responses from wrist flexors and extensors to mechanical perturbation of the contralateral wrist, and normal scalp distribution of somatosensory evoked potentials to right and left median nerve stimulation. Our findings are consistent with aberrant organization of motor representation areas and corticospinal pathways with ipsilateral as well as contralateral control of voluntary movement. 