Considerable progress has been made toward improving survival for children with brain tumors, and yet there is still relatively little known regarding the molecular genetic events that contribute to tumor initiation or progression. Nonrandom patterns of chromosomal deletions in several types of childhood brain tumors suggest that the loss or inactivation of tumor suppressor genes are critical events in tumorigenesis. Deletions of chromosomal regions 10q, 11 and 17p, and example, are frequent events in medulloblastoma, whereas loss of a region within 22q11.2, which contains the INI1 gene, is involved in the development of atypical teratoid and rhabdoid tumors. A review of the cytogenetic and molecular genetic changes identified to date in childhood brain tumors will be presented.