To determine the incidence of contralateral hernia development after unilateral inguinal hernia repair in girls, collected case series from two large hospitals were analyzed retrospectively. Among the 294 girls who had analyzed repair of a unilateral inguinal hernia (during a 15-year period), 245 could be traced; the mean follow-up period was 8.4 years. In 25 (10.2%) of the patients, contralateral hernia developed, mostly within one year (4 months to 6.5 years). The incidence of contralateral hernia development with respect to the original side of the inguinal hernia was significantly higher (19%) for the originally left-sided hernias than for the right-sided ones (6%) (P < .01). Although the incidence of contralateral hernia development for girls with a left inguinal hernia decreased as age increased, it was still 14.9% for the girls age 3 and up. Contralateral exploration should not be routine for girls who have a right-sided hernia, at any age. For left-sided hernias, it may be performed routinely for girls up to 2 years of age, and selectively for older patients.