tBackground: Noroviruses (NoV) have been shown to be an important cause of morbidity and mortalityin children worldwide, only second after Group A rotaviruses (RVA). In Paraguay, acute gastroenteritis(AGE) is the third cause of mortality in children ≤5 years old.Objectives: To analyze the presence and diversity of NoV in Paraguayan children ≤5 years old presentingAGE.Study design: Three hundred seventy eight fecal samples, negative for pathogenic bacteria and RVA, werecollected from children admitted as ambulatory and hospitalized patients in a large private hospitalfrom Asuncion, Paraguay from 2004 to 2005. The presence and diversity of NoV was determined by twodifferent RT-PCR strategies and nucleotide sequencing.Results: One hundred and sixty one samples were positive for NoV by partial amplification of the viralpolymerase gene (RdRp). No seasonality or differences in the viral prevalence for the different age-groupswere detected. GII and GI NoVs were associated to 58% and 42% of the infections, respectively. The geno-type was determined in 18% (29/161) NoV-positive samples. The genotypes detected were: GII.4 (18%),GII.17 (18%), GII.6 (14%), GII.7 (14%), GII.3 (10%), GII.5 (3%), GII.8 (3%), GII.16 (3%), GI.3 (14%) and GI.8 (3%).Amplification of the ORF2 from the GII.4 strains showed the presence of a new GII.4 variant.Conclusions: The results showed a continuous circulation of NoV in children throughout the two years ofstudy and an extensive diversity of genotypes co-circulating, highlighting the need for better surveillanceof NoV in Paraguayan children.