To clarify the phylogenetic relatedness of rotaviruses causing gastroenteritis in children and adults, an epidemiologic investigation was conducted in Mymensingh, Bangladesh, during the period between July 2004 and June 2006. A total of 2,540 stool specimens from diarrheal patients from three hospitals were analyzed. Overall, rotavirus-positive rates in children and adults were 26.4 and 10.1%, respectively. Among the 155 rotavirus specimens examined genetically from both children and adults, the most frequent G genotype was G2 (detection rate: 54.0 and 47.6%, respectively), followed by G1 (21.2 and 26.2%, respectively), and G9 (15.9 and 9.5%, respectively). G12 was also detected in five specimens (3.2% in total; four children and one adult). Sequence identities of VP7 genes of G2 rotaviruses from children and adults were higher than 97.8%, while these Bangladeshi G2 viruses showed generally lower identities to G2 rotaviruses reported elsewhere in the world, except for some strains reported in African countries. Similarly, extremely high sequence identities between children and adults were observed for VP7 genes of G1, G9 and G12 rotaviruses, and also for the VP4 genes of P[4], P[6], and P[8] viruses. Rotaviruses from children and adults detected in this study were included in a single cluster in phylogenetic dendrograms of VP7 or VP4 genes of individual G/P types. Rotaviruses with two emerging types, G9 and G12, had VP7 genes that were phylogenetically close to those of individual G-types recently reported in Bangladesh and India and were included in the globally spreading lineages of these G-types. These findings suggested that genetically identical rotaviruses, including those with the emerging types G9 and G12, were circulating among children and adults in city and rural areas of Bangladesh.