Blastic plasmacytoid dendritic cell neoplasm was previously known as natural killer (NK) cell leukaemia/lymphoma. This is a highly aggressive, historically difficult-to-diagnose haematologic malignancy with a poor prognosis. As understanding of the biology and origin of this type of cancer has improved, the World Health Organization (WHO) established the term blastic plasmacytoid dendritic cell neoplasm (BPDCN) in 2008. BPDCN is currently listed as its own category in the 2016 World Health Organization revision. Most often, BPDCN presents with features of both lymphoma and leukaemia. Little data is available about BPDCN and there is no standard approach to treatment.