Ventriculoperitoneal shunt (VP shunt) for hydrocephalus is thought to inhibit the closure of processus vaginalis by increasing intraabdominal pressure, thus it promotes the inguinal hernia. We reviewed the incidence and characteristics of the inguinal hernia in VP shunted patients, and tried to estimate the patency rate of processus vaginalis in early childhood. A reprospective review of patients undergone insertion of VP shunt between January 1980 and May 1998 at Seoul National University Children Hospital was done. 262 patients were included in this study. Among them, 28 patients developed inguinal hernia (10.7%). Six patients developed inguinal hernia before the insertion of VP shunt. According to the age of VP shunt, the inguinal hernia developed in 16.2% (12/74) of patients who had undergone VP shunt before 6 months old, 12.4% (11/89) between 6 months and 2 years old and 5.1% (5/99) after 2 years old. Among 22 patients excluding 6 patients who developed hernia before VP shunt, the incidence of inguinal hernia after VP shunt was 8.6% (22/256) with male predominance (M:F=18:4). 8 patients developed inguinal hernia bilaterally (36.4%). It is suggested that at least 14% of processus vaginalis is patent until 2 years old.