Abstract In penetrating wounds and crushing injuries involving the chest and the abdomen, rupture of the diaphragm may be difficult to diagnose and is easily missed. Strangulation and obstruction may occur at any time in a previously undiagnosed traumatic diaphragmatic hernia or it may present with acute pain in the chest and collapse due to perforation of a displaced viscus into the chest, a clinical appearance mimicking myocardial infarction. Severe pain in the shoulder and neck may occur due to irritation of the phrenic nerve; anorexia, vomiting, or disabling dyspnoea which may be sudden or of gradual onset over years may also be presenting signs. The dome of the diaphragm may be torn transversely or obliquely. Occasionally complete detachment of the periphery of the diaphragm and rupture of the central tendon and pericadium may occur. Eight cases of complications following undiagnosed traumatic diaphragmatic hernia are discussed. The importance of searching for a previous history of injury to the chest is stressed. The transthoracic approach for treatment in such cases seems the most suitable.