In 28 patients with spasmodic torticollis dorsal branches of the cervical nerves C1–6, and in 25 of these patients fascicles of the contralateral accessory nerve were investigated by light and electron microscopy. Significant changes were noted in 15 patients. The alterations were not seen or were less prominent in the 5 control cases studied for comparison. Semiquantitative evaluation of light microscopic findings revealed in 12 cases prominent and numerous Renaut bodies; in 9 cases evidence of regeneration (in 3 of these postoperatively); and in 11 cases disproportionately thin myelin sheaths in relation to axon calibers. In conjunction with endoneurial edema and thickening of the perineurium, these changes were suggestive of compression neuropathy. Whether these changes were the cause, or a side effect of the abnormal muscle contractions in spasmodic torticollis could not be elucidated. Peripheral nerve compression, however, may trigger abnormal activity in the peripheral part of the involved interneuronal circuits and may, thus, be considered as one of the many possible causes of spasmodic torticollis.