Diaphragmatic disease is often discovered in AOC. However, pre-operative assessment with CT imaging is not reliable in accurately detecting diaphragm involvement. Therefore, all patients with AOC should be regarded as in potential need for diaphragm surgery and their operation undertaken in cancer centres with adequate expertise in upper abdominal surgery. If there is a suspicion of diaphragm muscle invasion during diaphragmatic peritonectomy, the muscle should be partially resected. This will lead to potential upstaging of disease to stage 4A and therefore, to suitability for targeted therapy. In our Centre, the surgical removal of diaphragmatic disease did not significantly increase surgical morbidity.