The purpose of this study was to define the spectrum of hematologic neoplasms and chromosomal breakpoints associated with del(5q); separate analyses were performed to account for prior cytotoxic treatment. A total of 358 consecutive del(5q) cases were identified; specific diagnoses included myelodysplastic syndrome (MDS; 53%), acute myeloid leukemia (AML; 22%), plasma cell proliferative disorder (PCPD; 9%), myeloproliferative disorder (MPD; 7%), acute lymphoblastic leukemia (ALL; 2%), PCPD with MDS (2%), MDS/MPD (2%), and malignant lymphoma (ML; 2%). The corresponding figures in the absence/presence of prior cytotoxic treatment (n=250/108) were 61%/34% for MDS, 24%/19% for AML, 4%/20% for PCPD, 6%/8% for MPD, 1%/4% for ALL, and 2%/4% for ML. del(5q) occurred as the sole cytogenetic abnormality in 88 cases (25%) including 76 without prior cytotoxic therapy. Among the latter, 82% had MDS, 8% AML, 5% MPD, 4% PCPD, and 1% ML. Chromosome 5 breakpoints included q13q33 in 49% of the cases, q15q33 in 22%, q22q33 in 8%, and q13 in 3% and their distribution was not affected by specific diagnosis or treatment history. del(5q)-associated lymphoid disorders featured a higher prevalence of previous cytotoxic therapy and smaller number del(5q)-positive metaphases, when compared to their counterparts with myeloid neoplasms. We conclude that del(5q), although most prevalent in MDS, is seen across the spectrum of myeloid disorders including MPD and its occurrence in lymphoid disorders might signify, for the most part, an occult myeloid clone.