We investigated chromosomal aberrations in 16 patients with astrocytic tumors of various histologic malignancies by comparative genomic hybridization (CGH). The degree of chromosomal loss was shown to be negatively correlated with histologic malignancy. Losses of portions of chromosomes 1p, 19q and 22q were the three chromosomal aberrations observed most frequently. Alterations in multiple chromosomes were observed more frequently in glioblastomas than in astrocytomas or anaplastic astrocytomas (P < 0.001). Primary glioblastomas showed a high frequency of genomic DNA gains (5/7), whereas recurrent glioblastomas from anaplastic astrocytomas did not (0/3). We found CGH to be a powerful tool for surveying DNA alterations in tumors and characterizing the biology of tumors of astrocytic lineage.