The first rotavirus vaccine was associated with a small, albeit statistically significant, risk of intussusception in immunized infants. Before results of new vaccine studies are available, we need to define the real background risk of intussusception in participating countries. A 5-year retrospective study conducted in Panama found an average rate of 1 case per 3300 infants younger than 1 year of age, with substantial yearly variations ranging from 1:2500 to 1:5000.