The outbreak of gastroenteritis among children younger than 5 years of age between December 2000 and February 2001 represented an exaggerated rotavirus season. The surveillance activity after the outbreak suggests that rotavirus is the most common cause of diarrheal disease in El Salvador. Further surveillance could provide a sound basis for improving the response to epidemics of gastroenteritis and could provide data needed to decide whether rotavirus vaccination should be included in the national program for childhood immunizations.