Twenty cases with 32 cerebral aneurysms in eight families of familial intracranial aneurysms are presented. The present 20 cases, 191 cases in 81 pedigrees in the prior 48 reports and our 692 cases of nonfamilial intracranial aneurysm are analyzed from the view points of sex incidence, age at onset, location of aneurysm, incidence of multiple aneurysms and familial relationship. In addition, the heredity of familial intracranial aneurysm is discussed. The characteristics of our 20 cases are summarized as follows: (1) Mean age of our cases was 53.8 years but it differed from that (41.7 years) of the prior cases. (2) However, five patients (25.0%) were diagnosed at younger age (under 39 years) as in the previous reports. (3) The incidence of multiple cerebral aneurysms was very high (40.0%). (4) Middle cerebral artery aneurysms showed a higher incidence (50.0%). Furthermore, we observed the familial incidence (0.7 - 3.2%) in the total intracranial aneurysms encountered at the same neurosurgical unit, the incidence (39.5%) of cerebral aneurysm among children in parent-children cases and that (44.4%) among siblings in sibling cases of familial intracranial aneurysm. Therefore, we suggested the possibility of incidental aneurysm in the remaining siblings in the cases of familial occurrence.