In this discussion of the pathophysiology of generalized seizures, the authors conclude that current evidence supports a primarily cortical origin, and that there is a continuum between strictly partial seizures at one end of the spectrum and definite generalized seizures at the other. Typical interictal electroencephalogram (EEG) patterns seen in patients with generalized seizures and their clinical correlations are discussed, and the ictal EEG patterns are subdivided according to their relationship to interictal EEG patterns. Special tests, such as sleep, photic stimulation, hyperventilation, evoked potentials, computer analysis, and prolonged EEG video-monitoring, which enhance diagnostic ability, are reviewed.