Using comparative genomic hybridization (CGH), we have identified and mapped regions of DNA amplification in primary and metastatic osteosarcomas. Samples were obtained from four patients and ten independent xenografts. Sixty-four percent of the tumors showed increased DNA-sequence copy numbers, affecting 23 different chromosomal sites. Most of these regions were not previously associated with the development and/or progression of these tumors. Amplicons originating from 1q21-q23, 6p, 8q23-qter, and 17p11-p12 were observed most frequently. The 6p and 17p11-p12 amplicons seem to be specific for osteosarcomas, indicating that these regions may harbor genes relevant for the development of these tumors.