Although a familial tendency to develop brain tumors in the absence of well-recognized hereditary disorders is an important issue, it has been rarely reported. Studies of the familial occurrence of gliomas have yielded conflicting results. This phenomenon may be imputable to chance or environmental or hereditary factors. Furthermore, epidemiological and genetic investigations are fundamental to evidence of whether hereditary factors are active in the development of these tumors. We describe a group of six families, in each of which more than one member had glioma, and discuss the probable mechanisms of oncogenesis in familial tumors in light of the pertinent literature.