Gene markers or biomarkers can be used for diagnostic or prognostic purposes for all different types of complex disease, including brain tumors. Prognostic markers can be useful to explain differences not only in overall survival but also in response to treatment and for development of targeted therapies. Multiple genes with specific types of alterations have now been identified that are associated with improved response to chemotherapy and radiotherapy, such as O(6)-methylguanine methyltranferase (MGMT) or loss of chromosomes 1p and/or 19q. Other alterations have been identified that are associated with improved overall survival, such as mutations in isocitrate dehydrogenase 1 (IDH1) and/or isocitrate dehydrogenase 2 (IDH2) or having the glioma CpG island DNA methylator phenotype (G-CIMP). There are many biomarkers that may have relevance in brain tumor-associated epilepsy that do not respond to treatment. Given the rapidly changing landscape of high throughput "omics" technologies, there is significant potential for gaining further knowledge via integration of multiple different types of high genome-wide data. This knowledge can be translated into improved therapies and clinical outcomes for patients with brain tumors.