Closed chest trauma occasionally results in the development of traumatic lung cyst or pulmonary hematocele. Radiologically, this latter rarely mimicks posterior mediastinal mass, which can cause unnecessary surgical resection, We encountered two cases of pulmonary hematocele simulating posterior mediastinal mass. Multiplicity of the lesion, fracture of surrounding bony structure, decrease of mass size at follow-up examination, an acute angle between the mass and chest walL peripheral rim enhancement of the mass, as seen on CT scans, or characteristic signal intensity suggesting hematoma, as seen on MR images, helped differentiate pulmonary hematocele from posterior mediastinal mass.