SUMMARYEleven glioblastomas were submitted for chromosome analysis. Satisfactory cells were obtained from 3 as fresh tumor tissue and from the remainder after short periods in cell cultures. The predominant pattern was a near-diploid karyotype, with most frequent deviations occurring in Group 6-12. A review of earlier reports and results of the present study indicate the frequent occurrence of the above pattern in glioblastomas, with some tumors also containing an additional population of near-tetraploid cells. One established glioblastoma cell line had a hypotriploid karyotype and 4 marker chromosomes.