The history and development of the fanciful terminology concerning the structures of the limbic system are discussed. The diseases involving the limbic system are divided into three groups; (1) diseases in which the limbic system is more or less selectively involved, such as limbic encephalitis, herpes simplex encephalitis, cerebral confusions by the falx and tentorium, and internal herniations through the falx and tentorium; (2) diseases in which the limbic system is predominantly involved, such as arhinencephalia, holoprosencephaly, cyst of cavum septi pellucidi, Pick's disease, Alzheimer's disease, hippocampal sclerosis, and vascular diseases of the hippocampal formation; and (3) diseases in which the limbic system is randomly involved, such as various types of neoplasms and vascular and inflammatory lesions. The relationship between destructive lesions of the hippocampus and memory also is emphasized.