Ventriculoperitoneal shunt(VP shunt) for hydrocephalus is thought to inhibit the closure of processus vaginalis and promote inguinal hernia by increasing intraabdominal pressure. To estimate the patency rate of processus vaginalis and the incidence and characteristics of the inguinal hernia, 262 cases of VP shunt in early childhood between January 1980 and May 1998 at Seoul National University Children Hospital were reviewed retrospectively. Inguinal hernia developed in 28 cases(10.7 %), but six patients had an inguinal hernia before the VP shunt was placed. Patients who had a VP shunt before 6 months of age developed inguinal hernia in 16.2 %(12/74) of cases, patients shunted between 6 months and 2 years had an incidence of 12.4 %(11/89) and only 5.1 %(5/99) of patients operated upon after 2 years of age developed hernias. Twenty-two patients out of 256 cases (8.6 %) developed inguinal hernia after VP shunt, with male predominance(M : F=4.5:1). Eight patients developed inguinal hernia bilaterally(36.4 %). It is suggested that at least 14% of processus vaginalis is patent until 2 years old.