Rotavirus (RV) is the leading cause of severe gastroenteritis (GE) in young children. The cumulative risk of GE hospitalizations and hospital stays of < 24 hours is 1/25, which would amount to 13,600 Canadian children < 5 years. The incidence of nosocomial RV infections is an average of 8/10,000 patient-days in children < 5 years. An immunization program with a live-attenuated monovalent oral RV vaccine (RV1 - Rotarix® from GSK) will be implemented, free of charge, in the Province of Quebec in November 2011. To provide an accurate portrait of the disease and give critical information to the public health agencies as they struggle to control costs, we aim to evaluate the accuracy of surveillance for RV and other diseases with similar characteristics; estimate selection bias in passive laboratory-based surveillance; and estimate the agreement between surveillance time-series created from passive and active surveillance data sources.