Purpose: Familial glioblastoma multiforme (gbm) has been described in children with hereditary tumor syndromes. The occurrence of gbm in adult members of the same family and in the absence of tumor syndromes is extremely rare. We describe the cases of a brother and a sister with multifocal gbm diagnosed at the age of 63 years. We discuss three further paired gbm in adult patients from the literature. Patients and results: The sister was diagnosed with multifocal primary gbm in 2014 at the age of 63 years and 6 months. In 2018, her younger brother had to be operated on for a multifocal primary gbm at the age of 63 years and 9 months. Extended neuropathological examination revealed most markers to be similar, except for the percentage of O6-methylguanine-DNA methyltransferase promotor methylation, the presence of intratumoral immune cells and the immunohistochemical expression of C12ORF75. Comparison with further published cases of familial adult GBM reveals that most of these patients are male, about 65 years old and the tumor is localized predominantly in the left temporal lobe. Conclusion: Paired adult familial gbm occurs mainly in the elderly male patient with an integrative diagnosis of primary gbm. Whereas a statistical coincidence seems to be most likely in these rare cases, supplementary and improved genetic studies may identify pathogenetic causes of gbm.