Contralateral groin exploration (CGE) in children with unilateral inguinal hernia remains controversial. Between January 2002 and December 2007, 1967 pediatric patients with inguinal hernia were treated by two surgeons with different criteria of CGE (group A; boys younger than 2 years, older boys prematurely delivered, and all girls, B; birth weight lower than 2kg with inguinal hernia presentation within 6 months after birth, and suspicious physical findings) at Samsung medical center. Patient's age, sex, body weight, diagnosis, and metachronous contralateral inguinal hernia (MIH) incidence were analyzed retrospectively. Among 895 patients in group A, CGE was performed in 460 patients (66.4%) and MIH incidence was 1.7%. In group B, 31 patients (3.5%) had CGE among 1072 patients, and MIH incidence was 4.2%. The average hospital costs of group A and B were 763,956 won and 500,708 won, respectively. The CGE criteria of group B had advantage in total hospital cost. The primary site and the age at presentation had a signiticant effect on the incidence of MIH. But MIH incidence was low and the more contralateral explorations lead to increase of total costs. Therefore, routine contralateral groin exploration and surgery for a patent processus vaginalis could not be justified.