Polymethylmethacrylate (PMMA) is a self-curing acrylic resin that can be used in the repair of cranial defects. It is available in three forms: PMMA without mesh, PMMA reinforced with mesh, and PMMA preformed to fit a defect. In cranioplasty, the size and location of the defects provide the selection criteria for the use of PMMA. PMMA without mesh is ideal for small defects (5 cm2-15 cm2). PMMA reinforced with mesh is used for moderate sized defects (16 cm2-49 cm2). For very large defects (> or = 50 cm2), a CT scan guided mold is recommended because it provides the ideal contour and shape that simulates the normal skull.