Tumour origin and evolution currently is viewed as comprising a series of specific genetic events that take place in target cells and their clonal descendants. These events can be recognized at two levels: cytogenetic and molecular. The genetic results can be used as diagnostic and prognostic markers of neoplastic diseases. However, till now reports on the karyotypic characteristics of brain tumors are far from numerous. The most frequent cytogenetic alterations observed in primary brain tumors are losses or gains of chromosomes or chromosomal regions and presence of double minute chromosomes. Enhanced expression of several cellular oncogenes on human glioma cells lines were observed also.