This work addresses the controversial topic of the exploration of the contralateral side in the presence of a one-sided inguinal hernia in infancy. In a prospective study of 368 children with one-sided inguinal hernia, we demonstrated the consecutive development of a contralateral hernia in 22 (6%) of the children. We found that the child's age at first operation represents a risk factor for the development of a consecutive hernia. At an age of less than two months we found a highly significant (P < 0.0001) accumulation of consecutive hernias. These consecutive contralateral hernias appear significantly often (P < 0.0009) within the first two post-operative months in children at least two months old. In view of these findings, we see an indication for routine simultaneous repair on both sides for children aged less than two months at first presentation.