Partial motor seizures occur, followed after a variable interval by well-localized myoclonic jerks, in the patients with Kojewnikow syndrome, or epilepsia partialis continua. However, the epileptogenic focus remains to be established. We studied the epileptogenic focus of a 17-year-old boy with intractable Kojewnikow syndrome. Interictal EEG, ictal EEG, jerk-locked averaging, and ictal SPECT revealed a left central focus. A giant SEP indicated increased exitability of the primary sensory area. Magnetoencephalogram (MEG) and electrocorticogram identified the epileptogenic focus in the pre- and post-central cortex, indicating involvement of both the primary motor and sensory areas. Surgical treatment was successful. Thus, MEG proved to be the most accurate tool in the presurgical evaluation.