Congenital diaphragmatic hernia (CDH) is a rare anomaly (1 of 2-4000 live births) where abdominal organs can enter the thoracic cavity. It is usually diagnosed shortly after birth, often associated with pulmonary hypoplasia and pulmonary hypertension causing life threatening condition. In approximately one out of four patients CDH is diagnosed later in life, usually within several weeks or months from birth. CDH diagnosed in adulthood is very uncommon. Here we describe a 45 year old previously healthy woman that was diagnosed with a large tumor in her right hemithorax, after having symptoms of chronic cough and chest pain for several months. At thoracotomy the tumor was found to be omentum covered with a hernial sac that had penetrated the chest through a small diaphragmatic hernia. Six months postoperatively she was doing well with no respiratory or abdominal symptoms.