Dicentric assay is the international gold standard for cytogenetic biodosimetry after radiation exposure, despite being very labour-intensive, time-consuming, and highly expertise-dependent. It involves the identification of centromeres and structure of solid-stained chromosomes and the enumeration of dicentric chromosomes in a large number of first-division metaphases of cultured T lymphocytes. The dicentric yield is used to estimate the radiation exposure dosage according to a statistically derived and predetermined dose-response curve. It can be used for population triage after large-scale accidental over-exposure to ionising radiation or with a view to making clinical decisions for individual patients receiving substantial radiation. In this report, we describe our experience in the establishment of a cytogenetic biodosimetry laboratory in Queen Elizabeth Hospital, Hong Kong. This was part of the contingency plan for emergency measures against radiation accidents at nuclear power stations.