Fourteen cases of space-occupying lesions in the borderland between the supra- and infratentorial territories are presented. These lesions include gliomas, metastatic lesions, a sarcoma, an A–V malformation, a “pinealoma”, a medulloblastoma, intracerebellar Hodgkin's disease, a chordoma, an aneurysm, and meningiomas. One of these two cases of meningiomas which arose from the free margin of the tentorium is especially noteworthy in that it was operated upon with a good result.A variety of angiographic, ventriculographic, and encephalographic signs are discussed. Greater or lesser degrees of specificity are assigned to these signs. The cases, selected for presentation from a large series, were chosen for their value in illustrating radiological signs of disease in the area of the tentorial notch.The subject of tentorial herniations is not discussed. The subject has been adequately covered in the recent literature.Some of the data obtained by one of us (M.M.S.) through a review of 21 cases of clivus chordoma are presented.