Essential thrombocythaemia (ET) and Waldenström macroglobulinaemia (WM) are two distinct disorders. Studies have reported several cases of myeloproliferative neoplasms (MPNs) with concomitant plasma cell dyscrasia. However, there were no reported cases of ET with concomitant WM to date. Here, we present a 55-year-old Chinese man with thrombocytosis and raised immunoglobulin level. Further investigations led to a diagnosis of ET and coexistent WM. Next-generation sequencing (NGS) of his bone marrow identified 3 mutated genes: JAK2 V617F, MYD88 L265P, and ATM F1036L. After being treated with pegylated interferon and low﻿-dose aspirin, his platelet count normalized and immunoglobulin M (IgM) level reduced. To the best of our knowledge, this is the first reported case of dual pathology ET with WM.