Norwalk virus (NV) is a prototype strain of the genus Norovirus in the family Caliciviridae. The human noroviruses have emerged as major agents of acute gastroenteritis in all age groups, but there are no vaccines or antiviral agents partly due to the absence of a cell culture system. We report the generation of cells expressing self-replicating NV RNA (NV replicon) following transfection of NV RNA bearing an engineered neomycin resistance gene into cell lines of human (Huh-7) or hamster (BHK21) origin. Expression of replicon RNA was significantly reduced in the presence of interferon (IFN)-alpha in a dose-dependent manner in the NV replicon-bearing cells, suggesting a role for innate immunity in the control of human norovirus replication. This stable NV replicon system should lead to new insights into norovirus replication, virus-host interactions, and approaches for the treatment of norovirus disease.