Arnold-Chiari malformation is genetic disturbance of development of nervous coil. It is incorrect localization of spinal cord and tonsils of cerebellum, under foramen magnum in canal of spinal cord. Hydrocephalon and spina bifida may accompany Arnold-Chiari malformation. Symptoms usually occur in early childish age. For the sake of depth of dislocation of back brain structures there are distinguished four degrees of this malformation. First degree is the lightest one, hydrocephalon does not accompany its and it is manifested last – often in adult age. In this article is described 51-year-old patient who were diagnosed at Neurology Ward because of disturbances of balance, dizziness and weakness of muscles power of right hand. Arnold-Chiari disorder has not been diagnosed in this patient up till now. Physical examination revealed walking on the widen basis, deficiency of movables of IV and V fingers of right hand, positive test of Romberg, weakness of sense in limbs, lost of deep and vibration sense of inferior limbs. Underdone diagnostic excepted sharp inflammatory changes, growing changes and vessel malformations also, and arteriosclerosis changes as well within central nervous system as peripheral nerves. Photos RTG of vertebral column of the neck did not revealed any disturbances. Only performed magnetic resonance of the head let us determine properly diagnosis. Patient was discharged from the hospital with recommendation to notification at a Neurosurgical Department to consider operating cure of present patology.