Bronchogenic cyst is not a rare disease, but cases of bronchogenic cyst in the diaphragm are rare. We report a case of intraphrenic bronchogenic cyst. A 68-year-old woman was pointed out a 30 mm tumor on the left diaphragm by chest computed tomography (CT) 12 years ago. Because the size of the tumor had been increasing for 12 years, she was hospitalized for surgery. The tumor in the left diaphragm was removed by thoracotomy. Histologically, the tumor was diagnosed as a intraphrenic bronchogenic cyst.