Among 23 cases of myeloproliferative neoplasms (MPNs) with an associated del(5q) seen at our institution, 14 (61%) fulfilled diagnostic criteria for primary myelofibrosis (PMF). Other diagnoses included polycythemia vera (PV; n=2), essential thrombocythemia (ET; n=1), post-ET myelofibrosis (n=1), systemic mastocytosis (SM; n=1), and MPN, unclassifiable (n=4). Compared to their del(5q)-negative counterparts, del(5q)-positive PMF cases were significantly more anemic (p<0.001) and thrombocytopenic (p<0.001). However, survival and leukemic transformation rates appear to be similar between the two groups. del(5q)-positive PMF was histologically characterized by a mixture of both small and monolobated megakaryocytes as well as large and bizarre megakaryocytes. When used, lenalidomide therapy induced hematological and cytogenetic remissions in del(5q)-positive PMF. The current study identifies PMF as another del(5q)-associated myeloid malignancy with characteristic megakaryocyte morphology.