This is a descriptive study of 19 families with glial tumors. Twelve were identified prospectively from 178 consecutive, unrelated adults and children with newly diagnosed gliomas seen at a regional cancer center between 01 Jan 89 and 31 Mar 91 (6.7%). There were 45 affected members (42 confirmed); 30 males, 15 females, ages 4 months-78 years (median, 44.5 years; mean, 38.9 years). Two families had four affected members, three families had three, and the others two. All confirmed tumors were supratentorial and all, save one, contained an astrocytic element. Three additional members of two families had other brain or neuroectodermal tumors. These families were not unusually cancer prone and did not appear to have neurofibromatosis, tuberous sclerosis, or colonic polyposis. There was no consistent pattern of inheritance.