Omental herniation through a diaphragmatic defect without involvement of the stomach is rare and has often been misdiagnosed as mediastinal lipoma. We herein report two cases of intrathoracic omental herniation through adiaphragmatic defect in patients that were misdiagnosed as a mediastinal lipoma at presentation. They both underwent successful laparoscopic diaphragmatic hernia repairs with full resolution of their symptoms. Doctors should pay attention to the differential diagnosis between diaphragmatic hernia and mediastinal lipoma when a fatty mass is found in the mediastinum at the magnetic resonance imaging (MRI) or computed tomography (CT) scan.