To determine the proportion of hospitalisations for gastroenteritis caused by rotavirus, we tested for rotavirus stool samples of all children under the age of five hospitalised for gastroenteritis between 1 December 1999 and 30 May 2000 in seven community and specialised hospitals in Quebec. Of 944 children hospitalised, 565 (59.9%) were screened for rotavirus and 405 (71.7%) tested positive. From December to April, the proportion of positive results rose from 51.6 to 78.1%. Compared with children whose test results were negative, children who tested positive presented vomiting more frequently upon admission (88.9 versus 60.4%) and needed IV fluids in greater proportion (94.1 versus 78.0%), but spent less time in hospital (2.8 versus 3.3 days). Aside from dehydration, no complications were noted. In Quebec, a large majority of winter and spring hospitalisations for gastroenteritis in children is attributable to rotavirus.