Ependymomas are glial tumors of the brain and spinal cord. The most frequent genetic change in sporadic ependymomas is monosomy 22, suggesting the presence of an ependymoma tumor suppressor gene on chromosome 22. Thirty-three pairs of matched normal and tumor specimens from ependymoma patients were genotyped using 12 polymorphic microsatellite markers spanning the long arm of chromosome 22. Allelic deletion was found in 12 of 33 tumors (36.4%). Eight tumors showed partial deletions and 4 tumors exhibited loss of the entire arm of 22q. We identified two common regions of deletion: one at 22q11.21-12.2 flanked by markers D22S420 and D22S300, and a second candidate region at 22q13.1-13.3 between D22S274 and D22S1149. The size of each region was 21.1 and 2.4 cM, respectively. Thus, our results suggest that one or more tumor suppressor genes associated with ependymoma may be present on chromosome 22. Comparison of these results with clinicopathological data indicate that allelic losses on 22q tend to occur more frequently in intracranial anaplastic ependymomas in children and intraspinal ependymomas in adults.