So-called cortical epileptic seizures, when studied with depth electrodes, are seen to be accompanied by marked involvement of many subcortical structures, depending upon the site or origin of the cortical discharge. The after-discharge from frontal, central, temporal, and occipital cortices spreads to different subcortical nuclei. Three main structural patterns of propagation may be distinguished: (1) from the frontal granular cortex to the caudate nucleus and to the contralateral frontal granular cortex and subsequently to many other subcortical structures, (2) from the central cortex to the ipsilateral putamen and tnalamus and to the contralateral homologous central cortex, and (3) from the temporal cortex to the amygdaloid hippocampus complex and its subcortical projection sites, namely the septum, hypothala-mus, and medial thalamic areas. Other subcortical nuclei participate in focal attacks much less consistently but may become involved in generalized seizures. The generalization of a convulsive seizure is usually associated with propagation of the discharge from one system to another. This concept of epileptic propagation through subcortical structures offers a possible explanation for many of the clinical phenomena seen in various types of seizures. Moreover, it introduces a mechanism whereby subcortical structures may be the primary site of what would appear to be a cortically-induced epileptic discharge.