SUMMARYInvestigating 136 cases of genuine epilepsy who have typical grand mal attacks both from the genetical and clinical standpoints, we succeeded in bringing about the following results:The cases of simple family features, such as those who have no hereditary taint except epilepsy in their family stocks, have generally simple clinical features, and their seizures are limited to the motor sphere, externally manouvering convulsive attacks. On the other hand, the cases of polymorphic family features, such as those who possess psychoses or psychopathic personality in their family stocks, have mostly polymorphic clinical features, and their seizures tend to reach beyond the motor sphere to the psychic one, externally manouvering clouded states, deliria, etc. The degree of deterioration in the latter cases is altogether less notable than that in the former.From these facts we may assume that genuine epilepsy belongs, not only clinically but also genetically speaking, to the heterogenous category. That is to say, it can be classified into two principal group of simple manifestation in both clinical and genetical respects (the nuclear group) and that of polymorphic ones (the peripheral group).