1. Between 1965 and 1974 146 patients with unexplained tetraspasticity were admitted and examined. In 123 cases extended neuroradiologic examination with myelography of the cervical spinal canal was carried out. A space occupying lesion was found in 59 cases: narrow spinal canal, protruding discs. In 64 cases no pathologic processes were seen radiologically. Comparison of both groups: no differences in clinical signs, history or findings. 2. Tetraspasticity alone was the leading sign in 30 cases. The legs were always more severely involved than the upper limbs. In 70% spasticity was more severe on the right. Further clinical analysis depends on additional signs, particularly paresthesiae, pain, disturbed joint-sense. Among the patients with protruding discs heart-and circulatory insufficiency is a little more common, but in the group without protrusion exogenous/endogenous metabolic conditions(intoxication, malabsorption) and neoplasms. -Protein content of CSF is raised equally in both groups, particularly albumin. This is probably due to reduced circulation of CSF. In 6 patients an internal hydrocephalus was found. 3. No single active causative factor could be found nor any familial relationship. In spite of increasingly extended diagnostic techniques no underlying condition could be discovered. Tetraspastic is a "polygenetic" reaction of the central nervous system without a final common path. The cases show that mechanical factors (cervical myelopathy) predispose locally to non-mechanical injuries.