Between September 1995 and August 1998, the incidence and diversity of the main human rotavirus genotypes (G1, G2, G3, and G4 and P, P, P, and P) among Irish children were determined by using established and adapted reverse transcriptase PCR-based genotyping methods. From a total of 193 rotavirus-positive specimens collected from nine hospitals we successfully identified the P type in 182 (94%) of the samples and the G type in 165 (85.5%) of the samples. Only four samples could not be assigned a G or P type. Two P types existed in Ireland, P (78%) and P (16%), and their relative incidence varied over the 3 years of this study. No P or P types were detected. G1 was the most predominant G type (55%), and the incidences of G2, G3, and G4 isolates were 15.5, 1, and 11%, respectively. Three percent of the samples tested had a mixed G type. A P and G type was assigned to 158 (81.8%) of samples. Of the typeable samples, G1 P was the most prevalent (65%), whereas G2 P (17%), G3 P (1%), G4 P (12%), and mixed types (all G1/ G4 P) (4%) were detected less frequently. In the third year a significant genotypic shift from G1 P to G2 P and G4 P was observed. During the study, we noticed that the inclusion of random primers during cDNA synthesis greatly increased the specificity of the PCR typing assays. No correlation was seen between the contributing hospitals and a specific genotype. In conclusion, the coverage of infection given by the recently licensed tetravalent vaccine would be significantly high in Ireland, although future monitoring of genotypic changes among Irish isolates should be encouraged.