Ring chromosomes have been found with some regularity as solid tumors have come increasingly under cytogenetic study. The full genetic content and significance of these rings remain unclear. Dermatofibrosarcoma protuberans, a tumor of the deep dermis, consistently has supernumerary ring chromosomes, sometimes as the sole detectable cytogenetic change. Using a modified method for comparative genomic hybridization and fluorescent in situ hybridization with a panel of various probes, we found that these ring chromosomes consistently contain the chromosome 22 centromere along with interstitial sequences from chromosomes 17 and 22, specifically from regions 17q23-24 and 22q11-12. The ring chromosomes in dermatofibrosarcoma protuberans are vehicles for a particular pattern of relatively low-level genomic amplification of selected sequences.