Bile duct tumors are rare and have poor prognoses. Natural killer (NK) cells are frequent in human liver and infiltrate these tumors but do not control their progression. Responses of NK cells are regulated by natural killer immunoglobulin-like receptors (KIRs), which interact with HLA class I ligands. We aimed to characterize the features of the KIR gene loci and their ligands in patients with bile duct cancer (BDC).