A traumatic pulmonary pseudocyst is a rare complication of blunt thoracic trauma. The clinical symptoms and signs are similar to other respiratory diseases, such as pulmonary tuberculosis. Therefore, a trauma history with the resulting radiologic and clinical findings is important for making a diagnosis. A 26-year-old male was admitted to our hospital due to cough for 3 days. The chest x-ray revealed diffuse infiltrations and a cavitary lesion at the left lung. His left chest had hit a tree as a result of motorcycle accident one day before admission. Initially, it was assumed that his symptoms and chest X-ray might be due to a tuberculosis infection. However, bronchoscopy revealed old blood clots at both lungs, particularly in the left lower lobe bronchus. A transbronchial lung biopsy showed alveolar hemorrhage. A traumatic pulmonary pseudocyst was diagnosed from his trauma history and these findings. Computed tomography of the chest performed 4 months later showed regression of the cavitary lesion.