Short-term cultures from 16 chondromatous tumors, 15 primary and one recurrent, were analyzed cytogenetically. Clonal chromosome aberrations were found in one of six benign tumors and in seven of ten malignant tumors. A chondroma had a complex translocation involving chromosomes X, 8, 12, and 13, as well as a deletion of the derivative chromosome 8. In the malignant tumors, monosomy 6 and 22 were observed in three tumors and monosomy 10, 11, 13, and 18 were observed in two tumors. In two of the three metastasizing tumors, del(5) (q13) and loss of chromosomes 6, 10, 11, 13, and 22 were common features. Structural aberrations of chromosome 1 were found in five tumors, of chromosomes 6, 12, and 15 in three tumors, and of chromosomes 4, 5, 9, and 20 in two tumors. We conclude that although considerable cytogenetic heterogeneity exists among chondromatous tumors, the karyotypic anomalies are still nonrandom.