Three patients are reported whose cranial dura mater and bones were penetrated by intracranial glioblastomas in the absence of previous craniotomy or radiotherapy. The gliomatous nature of the tumors was confirmed by localization of cytoplasmic glial fibrillary acidic protein (GFAP) of the neoplastic cells. Review of the literature disclosed only 15 glioblastomas, including the three cases, spontaneously penetrating the cranial dura mater and bones. These patients ranged in age from 3.5 to 70 years with an average age of 40 years. The male/female ratio was 5/8. Five glioblastomas were in the temporal lobes, three were in the frontal lobes, three were in the frontotemporal regions, two were in the occipital lobes, one was in the frontoparietal region, and one was in the temporoparietooccipital region. Six glioblastomas also had spontaneous distant metastases. In the absence of previous craniotomy and radiotherapy, rapid growth of the glioblastomas may promote such spontaneous penetration into the cranial dura mater and bones.