A 30-year-old man was admitted to the hospital 7 years after an automobile accident during which a lumbar vertebra was fractured. Immediately after the accident he had neither thoracic nor abdominal symptoms. An X-ray film obtained 4 years after the accident showed elevation of the left side of the diaphragm. That elevation progressed over the next 3 years, although the patient had no symptoms. On admission, a chest X-ray film showed blunting of the left costo-phrenic angle and mobility of the shadow, which simulated a pleural effusion. A chest CT scan and barium studies showed that portions of the small intestine, transverse colon and descending colon were in the left side of the thorax, but the diaphragm was not seen. The patient was given a diagnosis of delayed traumatic diaphragmatic hernia after T1-weighted sagittsal magentic resonance images revealed the whole diaphragm and the hernial orifice. Magnetic resonance imaging can be very useful in the evaluation of diaphragmatic hernia.