Cytogenetic abnormalities in patients with essential thrombocythemia (ET) are infrequent. Their role in survival of patients and disease transformation is not extensively studied. We describe cytogenetic abnormalities in 172 patients with ET at a single institution. At presentation nine (5.2%) patients had cytogenetic abnormality and three (1.7%) additional patients acquired them during follow-up. Survival of patients with cytogenetic changes at presentation did not differ when compared to the patients with normal karyotype. The more common were abnormalities of chromosome 9 (n = 4), 20 (n = 2), 5 (n = 2), and complex abnormalities (n = 2). Forty-one patients (23.8%) had additional cytogenetic tests performed for monitoring purposes during follow-up. Five patients (2.9%) with normal karyotype transformed to myelofibrosis (MF) without developing new cytogenetic changes at transformation. Two patients (1.2%) with normal karyotypes at presentation transformed to myelodysplastic syndrome and acute myeloid leukemia, respectively. Both acquired complex cytogenetic changes at the time of transformation. There is no rationale for repeating cytogenetic tests in ET patients on follow up, unless blood cell count changes suggest possible transformation.