The clinical and electrophysiological features of segmental myoclonus affecting the right arm and upper trunk are described in a patient with multiple sclerosis. Electrophysiological studies suggested that the myoclonus was propagated from a generator site in the cervical cord, where lesions were found using MRI. The spread of electromyographic activity in each myoclonic jerk was slow and variable. These findings are characteristic of propriospinal myoclonus, which has not been associated with multiple sclerosis previously.