The prognostic significance of cytogenetic findings at diagnosis in polycythemia vera (PV) was investigated in a retrospective series of 137 patients. Cytogenetics were normal in 117 patients (85%) and displayed a -Y abnormality in five patients (7% of male patients), and other chromosomal abnormalities in 15 patients (11%). The most frequent cytogenetic anomalies were trisomy 8 (n = 4), trisomy 9 (n = 2), deletion 20q (n = 2) and chromosomal 1 abnormalities (n = 2). Parameters that were significantly associated with abnormal cytogenetics included age > or = 60 yr (P = 0.02), but not JAK2V617F allele burden, thrombosis, hemorrhage, leukemic/fibrotic transformation, or survival. We conclude that cytogenetic anomalies occur infrequently at PV diagnosis and do not confer an adverse outcome.