The development of a malignant tumor generally entails a series of events that damage the genome of a somatic cell and result in the malignant phenotype. These events chronicle the malignant progression of a tumor; a dynamic process in which more aggressive and growth-deregulated cell populations are constantly evolving. Gliomas, the most common primary tumors of brain, are known to become increasingly malignant with time. Within recent years, several details of the molecular genetic events associated in their progression have been determined. The earliest events of glioma progression include loss of genetic information from the long arms of chromosomes 13 or 22, or the short arm of chromosome 17 for which targeting of the TP53 (p53) gene has been indicated. Loss of a single complement of type I interferon (IFN) genes from 9p and loss of genetic information from 19q are seen in the tumors of intermediate malignancy grade. Events associated with the most malignant of glial tumors include loss of the second, type I IFN gene complement, loss of genetic information from chromosome 10, and gene amplification (most commonly the epidermal growth factor receptor, in 40% of cases). These findings have helped elucidate the events associated with glial tumorigenesis, and through the identification of specific genes, have provided a starting point for investigating the molecular biology of central nervous system neoplasia.