Stools were evaluated from 5,811 patient visits for treatment of diarrhea in Matlab, Bangladesh, between June 1987 and May 1989. The stools were analyzed to determine the distribution of serotypes of group A rotaviruses (RV). A total of 898 stool samples (15.5%) contained RV, as determined by using an enzyme-linked immunosorbent assay. RV isolates from 855 of these samples were serotyped by using serotype-specific synthetic oligonucleotide probes. A total of 558 (65.3%) could be assigned to specific serotypes: 166 (19.4%), 228 (26.7%), 39 (4.6%), and 125 (14.6%) belonged to serotypes 1 through 4, respectively; 12 (1.4%) hybridized with more than one serotype; and 285 (33.3%) failed to hybridize. RV diarrhea was evident throughout the year, with peaks in the dry winter months and in September 1988, coinciding with a major flood. RV was isolated from 46.6% of patients between 7 and 12 months old. Among children under 24 months of age with RV diarrhea, 1.2% (10 of 828) died. The corresponding percentage for children with diarrhea from all causes is 0.9% (29 of 3,301).