A 23-year-old female was admitted to our hospital complaining of tremor in the upper extremities and gait disturbance. Beginning at age 18, this patient experienced tingling of the right fingers, gait disturbance, dysesthesia of both hands, and tremor in the upper extremities. These symptoms disappeared several weeks after each onset. At age 21, gait disturbance and coarse tremor in the upper extremities developed. They were exaggerated and occurred repeatedly. On neurological examination, the right optic disc was slightly pale. She had nystagmus in all directions with ocular movements. Deep tendon reflexes were hypoactive throughout. There was no tremor in the upper extremities at rest, but during the voluntary movements especially in maintaining certain posture coarse tremor developed. When performing goal-directed motion, such as finger-nose test, the tremor became worse near the terminal position. The patient's gait was broad-based, with the trunk trembling. There were no sensory disturbances, dysarthria, or bowel or bladder dysfunction. Laboratory studies were normal except for high IgG% in the cerebrospinal fluid. An electromyogram using surface electrodes recorded rhythmic bursts of about 4c/s, alternating between the extensor and the flexor muscles of the right arm. MRI of T2-weighted images showed many high-intensity areas located around the bilateral ventricles and near the area of the decussation of superior cerebellar peduncle. A diagnosis of multiple sclerosis was made in this case based on the patient's history of illness and MRI findings. The tremor in her right upper extremity was too intense and coarse to be described as tremor, and should better be called "hyperkinésies volitionnelles (HV)".(ABSTRACT TRUNCATED AT 250 WORDS)