Real-time RT-PCR, combining amplification and detection of virus-specific amplicons, is a promising tool for norovirus detection in environmental or food samples such as shellfish. We developed a real-time RT-PCR assay based on one-step detection using single primer sets and probes for norovirus genogroups I and II. Seventy and seven RT-PCR units of genogroup I and II reference norovirus strains, respectively, were detected in artificially contaminated oysters. Validation of the new method on 150 archived naturally contaminated shellfish confirmed the utility of the genogroup II primer set to detect a large range of different strains circulating in France since 1995, but genogroup I strains were detected infrequently.