A 19-year-old man developed progressive unsteady gait and speech disturbance two years ago. He recently noticed muscle twitches in the left limb. Neurological examination revealed scanning speech, saccadic ocular movement, ataxia of trunk and limbs predominant on the left side. Rhythmic myoclonus was present at rest around the left shoulder and arm, and amplified by raising the left arm. There was no myoclonus in the soft palate. MRI revealed only a cerebellar atrophy. This patient was diagnosed as having cortical cerebellar atrophy with rhythmic skeletal myoclonus (RSM). Tc-99m ECD SPECT showed a decrease in the blood flow of the right thalamus when the myoclonus was enhanced by raising the left upper limb, which suggests that the cerebello-thalamo-cortical system as well as Guillain-McIlaret triangle is involved in the development of RSM.