Natural killer (NK) cells are an important component of the immune response to a number of viruses; however, the molecular basis of how NK cells discriminate between healthy and virus-infected cells is largely unknown. Here, we show that expression of the immediate-early gene product ICP0 is sufficient to produce an increased susceptibility to NK lysis of herpes simplex virus (HSV)-infected cells. This effect does not depend on down-regulation of major histocompatibility complex class I molecules or on the induction of expression of ligands for the activating NKG2D receptor. Detection by NK cells of the changes in the target cell induced by HSV ICP0 gene expression depends on the natural cytotoxicity receptors (NCRs) NKp30, NKp44, and NKp46. To our knowledge, this is the first identification of a viral gene that triggers the up-regulation of cellular ligands for the NCR; moreover, these observations highlight the importance of the NCR for immunosurveillance of viral infection by NK cells.