Sudden death due to diaphragmatic hernia in an adult is exceptionally rare. A 43-year-old man was found dead by his cohabiting mother, lying supine on the floor in his house. He had complained of epigastric discomfort for 1 month, and respiratory symptoms occurred 1 day before his death. He had no history of trauma. Postmortem computed tomography scan revealed the enlarged fluid-filled stomach herniated into the left pleural cavity, compressing the left lung with a mediastinal shift to the right. At autopsy, the left pleural cavity was occupied by herniated abdominal contents with mediastinal shift. The herniation of the stomach, the whole spleen, a portion of the colon, and omentum into the left pleural cavity had occurred through a smooth oval 9 × 5-cm defect in the posterolateral part of the light diaphragm. The stomach was markedly distended and contained 1600 mL of yellowish brown liquid with food residue. Ischemic changes of the herniated organs were not observed. Death was attributed to respiratory failure from abdominal viscera herniation into the left pleural cavity.