Cytogenetic studies of 50 human gliomas, including three oligodendrogliomas, 16 grade I-III astrocytomas, and 31 glioblastomas multiforme, were performed using the short-term tissue culture method. The most common numerical chromosome aberrations were +7, -9, -10, -14, and loss of a sex chromosome. Structural changes involved predominantly the following chromosome arms: 1q, 2q, 6q, 7q, 9p, 14q, 17p, and 18p. Losses of chromosomes 9, 10, and 14, often occurring simultaneously and in polyploid clones, were observed almost exclusively in high-grade gliomas, and appear to constitute important events during glioma progression.