Norovirus has captured increasing attention as an agent of childhood diarrhoea. However, it is not known whether norovirus causes as severe diarrhoea as rotavirus, particularly among children in developing countries. In a 1-year study conducted between May 2004 and April 2005 in Recife, Brazil, norovirus was detected by ELISA in 34/233 (15%) diarrhoeal children less than 5 years of age. The severity of clinical illness, as indicated by the presence of dehydration, the requirement for hospitalization, and the duration of hospital stay, was similar between children with norovirus and rotavirus infection. These data underscore the importance of norovirus as a cause of severe diarrhoea in children.