Noroviruses cause acute viral gastroenteritis worldwide. They are classified in five genogroups, of which GI, GII, and GIV infect humans. Little information is available on the prevalence and clinical effects of GIV noroviruses. We conducted a large-scale molecular-epidemiological investigation, a yearlong monitoring of 11 wastewater treatment plants throughout Italy, with the aim of studying the circulation of GIV NoV, as well as its genetic diversity. Eight percent of samples tested positive, and sequence analysis showed a considerable degree of genetic variability. These results imply the need for further studies to elucidate the role of this virus as a gastroenteritis-causing pathogen.