As is well known, the typical case of LINDAU'S tumor consists in angioma and the special group of cells constituting reticular structure between them and often apt to change into pseudoxanthomatous cells. Such a structure of this tumor, together with the cyst formation often accompanying the tumors sharply differentiates them from angiomata of other organs. The first description by LINDAU concerned with primary tumor of the cerebellum, but later experiences have revealed that the same tumor he has described come forth also in the cerebrum, the medulla oblongata and the spinal cord as weIl, though more rarely.Here, it must be noted that the angiomata of this type are almost always located in the cortex directly under the arachnoid or subcortex and that they are frequently accompanied by angiomatosis retinae of the eye (HIPPEL'S disease) and other tissue malformations of the liver, the spleen, the lung, the kidney and the pancreas. There are many names proposed for this type of tumor, such as angioreticuloma, angioblastoma and various others-a diversity suggesting the disagreement of opinions of the tissue structure, the histogenesis and the entity of these tumors.Among the numerous names proposed, the two cited in full above are the most commonly used, the latter based on the assumption that the cells in question found in the stroma of the tumors are angioblasts, while the former comes from the idea that these cells are reticulum cells. We have, however, few descriptions to give support to such assumptions, and what is more, we may say no explanation as to why such angiomata of a specific type appear in the central nervous system alone has been ever given. The authors of this paper have obtained a number of interesting informations in treating a case of cerebellar tumor, though not yet accompanying macroscopically visible cyst formation, showing a histologically typical structure of LINDAU'S tumor, and studying these informations with the data obtained from 2 cases of such tumors previously reported from this laboratory, have arrived at some tentative conclusions on the structure and histogenesis of these tumors, on which we will report in the following.