To date, very few cases with intraneural ganglion cyst of the peroneal nerve has been reported. The common symptoms include localized pain and various degrees of motor and sensory deficits. Though electrodiagnostic study has been useful in lesion localization, recent imaging studies, such as ultrasonography and magnetic resonance imaging, should be used in establishing differential diagnosis and extent of a lesion preoperatively. Treatment can be achieved by microsurgical removal of the cyst. We had a 74 year old female with right foot drop for 3 months and we diagnosed that she had intraneural ganglion of the peroneal nerve using physical examination, electrodiagnostic study, ultrasonography, and magnetic resonance imaging. Although there was no specific symptom on the left side, there was a similar lesion like that of right intraneural ganglion, that was detected by ultrasonography. However, the patient's neurologic symptoms have not improved after operation. (J Korean Acad Rehab Med 2006; 30: 289-293)