Introduction. Traumatic diaphragmatic hernias occur after blunt or penetrating trauma. The case reported in this article is an incidental and unusual diagnosis in clinical practice. Case. We report a woman with a history of thoraco-abdominal trauma from a road accident that occurred 30 years ago. In the chest X-ray we found a radioopacity in the right lung base resulting from a respiratory infection. The image persisted in spite of effective treatment for the underlying respiratory condition, which made us suspect a diaphragmatic hernia corroborated by computed tomography. Discussion. A high level of suspicion is essential for the initial evaluation of patients with blunt or penetrating thoraco-abdominal trauma. Conclusions. Traumatic diaphragmatic hernias constitute a clinical challenge both for diagnosis and surgical treatment.