Objective: the authors aim to establish a DNA sequencing procedure for detection of CALR mutations in Vietnamese patients with essential thrombocythemia, facilitating an effective diagnosis approach. Patients and methods: the authors analyzed CALR mutations from 8 essential thrombocythemia patients without JAK2 mutation. Exon 9 of CALR was amplified by polymerase chain reaction, followed by DNA sequencing using ABI 3130 Genetic Analyzer. Results: CALR mutations were detected in 4 patients, including deletion of 52 nucleotides (c.1099-1150del) in 2 patients, and insertion of 5 nucleotides (c.1154-1155insTTGTC) in other 2 patients. Conclusion: DNA sequencing can detect CALR mutations for diagnosis of Vietnamese patients with essential thrombocythemia.