Reconstruction of cranial defects can be reasonably considered a failure if an aesthetically obvious cranial contour deformity persists after surgery. Such unsatisfactory outcome often results from variable resorption of bone grafts or infection, requiring removal of implant. In considering further treatment for such failed cases, the use of alloplastic implants is frequently warned as imprudent due to their theoretically increased potential for infection; however, the validity of such caution has never been substantiated. We describe a user-friendly, time- and cost-effective method of producing prefabricated methyl methacrylate implants for the reconstruction of cranial defects, using readily available computer-aided design and computer-aided manufacture facilities. This method was carried out in 31 patients who presented with persistent cranial defects after previously failed cranioplasty. The efficacy of this technique and the clinical outcome of the patients in this series were analysed. All implants produced a precise fit, with a reduction in operating time and satisfactory cosmesis having been achieved. Infection that required removal of implant occurred in three patients (9.7%), and one patient developed a dural tear, requiring repair. Customised fabricated alloplastic implants provide a safe, accurate and efficient way of restoring normal cranial contours in patients with cranial defects who have had previous failed cranioplasties.