The diagnosis of occult inguinal hernia is difficult for those who have only pain in the inguinal region but no other obvious clinical symptoms. However, we found that inguinal peritoneography is an effective method to diagnose occult inguinal hernia with chronic pain in the inguinal region but no positive findings on physical examination. We selected 10 patients who complained of chronic persistent inguinal pain but had no positive findings on physical examination to undergo peritoneography on an outpatient basis. Peritoneography was performed using a midline or periumbilical approach, with the head elevated 20 to 30 degrees in a prone or lateral position, and the hernia was sometimes induced by manipulation during the operation, and then examined. The results showed that 6 out of the 10 patients with no positive physical examination were found to have an inguinal hernia by peritoneography, and underwent inguinal surgery to investigate the inguinal hernia; the inguinal hernia of the 6 patients was confirmed during the operation. We concluded that peritoneography is a safe and reliable test for the diagnosis of occult inguinal hernia.