We report an autopsy case of duodenal bulb obstruction caused by a shiitake mushroom. A 74-year-old woman with depression was admitted to the hospital after suffering nausea and abdominal fullness for 3 days. Because the physical findings and laboratory data on admission revealed marked dehydration, lactated Ringer's solution was administered. Twelve hours later, the patient suddenly died. Autopsy showed an enlarged stomach filled with 850 ml of partially digested food. In the anal side of the pylorus, a 9-cm-diameter shiitake mushroom had become impacted, causing complete obstruction. We conclude that the patient suffered from duodenal bulb obstruction caused by the impacted mushroom and subsequently died of ileus. This case illustrates a rare cause of duodenal obstruction and emphasizes that ingested food can cause obstructive ileus and death.