We present whole-head magnetoencephalographic recordings from a patient suffering from trigeminally triggered left-sided hemifacial convulsions. The patient was a candidate for surgical treatment, but regardless of extensive scalp EEG, videotelemetry and PET recordings, an epileptic focus could not be identified. Magnetic signal distribution during a seizure suggested focal epileptic activity in the face area of the right primary motor cortex. A secondary focus was activated 22 ms later in the left hemisphere. Discharges could be triggered by sensory stimulation of the left lower gum. The similarities of this seizure production mechanism to trigeminal neuralgia and kindling are discussed.