In total, 4,806 stool samples collected from 2003 to 2009 were tested for norovirus (NVs) RNA. A positive polymerase chain reaction (PCR) result was obtained from a total of 628 (13%) of the samples. Molecular analysis of strains from 64 outbreaks showed that there were up to 20 genotypes involved in the outbreaks. The dominant genotype throughout the study period was GII-4. In this study, NVs are an important cause of gastroenteritis in Seoul, Korea. By this molecular investigation, genotypic distribution associated with NVs infections will be used for control and prevention of NVs related diseases.