To assess the genetic diversity of rotavirus strains in Norway, the distribution of rotavirus genotypes was studied in children admitted to hospital with acute gastroenteritis. The detection of rotavirus in stool samples was compared using an enzyme-linked immunosorbent assay (ELISA), an immunochromatographic test and RT-PCR. Children <5 years of age admitted to hospital with diarrhea in three large hospitals were enrolled prospectively from March 2006 to February 2008. Rotavirus was detected in 58% of the children by the immunochromatographic test, in 63% by ELISA and 72% by RT-PCR. A total of 219 (70%) rotavirus isolates were characterized in order to determine the genotype. The predominant G types included G1 (53%), G9 (16%), and G3 (13%), and the frequency of G3 varied more than G9 between seasons (8-20%). The P[8] genotype was identified in 188 (86%) of samples, and the globally common genotype combinations G1P[8], G2P[4], G3P[8], G4P[8], and G9P[8] accounted together for >80% of infection. No unusual rotavirus strains were detected, and only four samples contained mixed infections. This study demonstrates that ELISA has similar specificity but lower sensitivity compared to RT-PCR. The immunochromatographic test had the lowest sensitivity and specificity compared to the other assays. Rotaviruses causing severe gastroenteritis leading to hospitalization of children <5 years of age in Norway include the common genotypes, however, a considerable geographical and seasonal variation was observed in the distribution of these genotypes. These data may be important for assessing the need for introducing rotavirus vaccines into immunization programs in Norway.