This study establishes the prevalence of Human Gene Mapping 11 (HGM11) chromosome abnormalities in bone marrow (BM) samples from 3,996 patients with malignant hematologic disorders. Examination of the karyotype of the stemline in these patients showed that 71.6% had one abnormality and 26.4% had two or more; the remaining 2.1% had two different abnormal clones. We observed 9,431 chromosome abnormalities, of which 56% were structural and 44% numeric, but these figures varied slightly with karyotype complexity. Because the HGM11 committee studied published cases with a single chromosome abnormality to identify potential "primary anomalies," we examined the karyotype from our 2,860 patients with a single abnormality in their stemline. We observed all but 12 of the 34 HGM11 numeric abnormalities. Except for 21 patients with a +Y, we did not observe two or more patients with any non-HGM11 numeric abnormality. We observed 91 of the 124 HGM11 structural abnormalities and noted 6 that were not listed by HGM11, and each of these occurred in two or more patients. Among patients with two abnormal clones, 34% had a t(9;22)(q34;q11), del(20)(q11q13), or +8. In 50% of the males with two abnormal clones, one of the clones was -Y. We attempted to create a reference table that lists HGM11 abnormalities in hematologic disorders and their frequency in our series, the reported associated disorders, and photographs of representative chromosome abnormalities.