Extrapleural pneumonectomy, which usually requires placement of a prosthetic hemidiaphragm, can be offered to approximately 24% of patients with malignant mesothelioma. Expanded polytetrafluoroethylene (Gore-Tex) has superior physical characteristics for diaphragmatic grafting and is the material of choice at the authors' institutions. This article describes conventional radiography and computed tomography findings in three patients who underwent extrapleural pneumonectomy. A freshly placed Gore-Tex prosthetic diaphragm appears as a radiolucent crescent-shaped band at the inferior border of the hemithorax and could be confused with a pneumoperitoneum. With time, the lucent crescent becomes thinner and eventually becomes radiopaque; it may be confused with a calcified diaphragm.