Rotavirus gastroenteritis was studied by enzyme-linked immunosorbent assay (ELISA) and by PAGE from April 1983 to April 1985 at the Buenos Aires Ricardo Gutierrez Children’s Hospital and at the San Justo Children’s Hospital. Based on examination of 576 cases, rotavirus was identified in 109 (18.9%) cases by ELISA and in 99 (17.2%) cases by PAGE. As a diagnostic tool PAGE presented a sensitivity of 90.8% compared with ELISA. Compared with the control SA-11 genome, 84 samples (84.9%) presented a long electropherotype and 15 isolates (15.1%) presented a short electropherotype. We detected 35 different long electropherotypes and report a short electropherotype that did not show genome variation and was responsible for an outbreak in the San Justo Children’s Hospital population from September 1983 to July 1984.