The karyotypes of 4 human ependymomas have been determined. In one ependymoma, translocations involving chromosomes 9, 17 and 22 were observed together with the loss of the normal chromosome 17. A second ependymoma had many chromosomal alterations that included a translocation between chromosomes 1 and 2 and re-arrangements involving chromosome 17. No major consistent alterations were detected in the remaining 2 cases. Our karyotypes do not resemble the few previously published karyotypes of ependymomas, but had features, such as the alterations involving chromosome 17, that were similar to those of other brain tumours in children.