Genogroup (G) IV norovirus (NoV) has been described in the literature as infectious agents in humans, although there are few reports regarding the frequency and spread of this virus, resulting in insufficient epidemiological data. The aim of this study was to investigate the occurrence of GIV norovirus in the State of Rio de Janeiro, Brazil in order to evaluate frequency, concentration, and genetic diversity using clinical and environmental approaches. For this purpose, 316 stool samples were collected from acute gastroenteritis cases reported over a period of three years. Wastewater samples were also obtained from the main wastewater treatment plant (WWTP) located in Rio de Janeiro throughout one year, totalizing 156 samples. All samples were submitted to quantitative analysis by TaqMan™ real-time PCR for GIV norovirus. Three out of 316 clinical samples were positive (0.9%) for GIV, with viral load ranging from 104 to 106 genome copies (CG) per gram. Regarding wastewater samples, GIV were detected in 52% of raw sewage, with viral load ranging from 104 to 106 CG per liter. Phylogenetic analysis revealed the circulation of a new GIV genotype in both clinical and environmental samples. To our knowledge, this is the first description of GIV norovirus in clinical samples in Brazil. These results demonstrate the importance of performing laboratory surveillance of clinical and environmental samples, assisting the comprehension of the epidemiology pattern of viruses with neglected diagnosis and indefinite impact in the population.