A case of asymptomatic Bochdalek's hernia in adult is reported. A 21-year old woman was pointed out having an abnormality on a chest X-ray film at screening. Barium enema, chest CT scan and MR imaging revealed a Bochdalek type diaphragmatic hernia. Operation was done by the abdominal approach, and the herniation of the colon and spleen to the thorax through the dorsolateral defect of the diaphragm was seen. Size of foramen was 10×8cm and hernia sac was not visualized. Adult Bochdalek' s hernia is relatively rate. This is the 96th reported case in the Japanese literature. The symptoms, operative method and operative findings were discussed.