Two cases of lipoma of the tuber cinereum, unexpectedly discovered in the course of autopsy examination, are reported. Each case was thoroughly investigated by serial sectioning of both the diencephalic floor and the tumor. Some peculiar findings observed and a complete survey of the literature revealed that such a growth may be considered an incomplete benign mesenchymoma, i.e., a mixed tumor of mesenchymal derivates, according to Stout (14). The error in development, consisting in the inclusion of embryonal germs of primitive meninx into the nervous system, may occur early during the third month of intrauterine life, at the time of the formation of the primitive septa.