Midline spikes are characterized by spike foci recorded at Cz, Fz, or Pz with amplitude ranging from 20 to 350 microvolts. Out of 7,929 EEGs performed at the Neurodiagnostics Laboratory, Kaiser Permanente Medical Center, Anaheim, California, between 1996 and 2006, 17 EEGs (0.21%) were identified as having interictal midline spikes with or without other epileptiform discharges. Eight EEGs showed midline spikes at Cz, 2 at Fz, 2 at Cz and Fz, 1 at Cz and C3, 1 at Cz, C3, and P3, 1 at Cz and F8, 1 at Cz and T4, and 1 at Cz with 2 Hz generalized spike and slow wave complex. Midline spikes were recorded in 10 males and 7 females. The age ranged from 4 days to 38-years-old with a mean age of 10.8 years. Twelve patients (70.6%) were children. Twelve patients (70.6%) had generalized tonic-clonic seizures and 5 had partial motor seizures. Of the 17 patients, 14 had no known causes, 1 had an agenesis of corpus callosum, 1 had a left frontal arteriovenous malformation, and 1 had a left frontal area stroke. We postulate that the mechanism for the genesis of midline spikes may be heterogeneous. Midline spikes may be triggered by thalamocortical network in a generalized tonic-clonic seizure, or may originate in the parasagittal cortex in a partial motor seizure.