Background: Coronal alignment may impact clinical outcome and survivorship in TKA. Patient-specific instrumentation was developed to restore mechanical or kinematic axis and potentially reduce component malpositioning. Although it is clear these instruments add cost, it is unclear whether they improve alignment. Questions/Purposes: We determined whether the mean mechanical axis before and after TKA performed with patient-specific instrumentation restored and whether there were any outliers or not. Also the new technique is evaluated by determining the operative timing, blood loss , the need of blood transfusion and the ability to perform bilateral TKA in the same setting. Methods: We prospectively evaluated 15 primary TKAs performed for osteoarthritis & rheumatoid arthritis using the patient-specific instrumentation technique aiming to restore the mechanical axis; calculated by the long leg film 6 weeks post-operatively. This new concept exploits the capability of using computer-assisted preoperative planning software to provide patient-specific instruments that could replace conventional instrumentation systems. Preoperative CT images are acquired and imported to a special software system that has three-dimensional data of the TKA implant to be used. Planning and possibly virtual surgery is performed on the computer before it is done on real patients. This includes sizing, alignment, bone cutting, and verification of optimal implantation and positioning. Two virtual templates, femoral and tibial cutting guides, are designed and then transformed into physical cutting guides using rapid prototyping technology. The guides have built-in information of the pre-operative planning that can be transferred to the patient’s knee when the guides are positioned on the matching surfaces of the distal femur and proximal tibia. Then, surgeons can use these guides to make all necessary initial cuts upon which the position of the conventional cutting blocks, would be chosen. Results: A group of statistical analysis and comparative studies between the pre-operative and post-operative mechanical axis, operative timing and technique evaluation are mentioned in the thesis. Conclusion: Patient-specific instrumentation for TKA shows improved accuracy of alignment and a significant reduction in blood loss and operating time , but the fraction of outliers was relatively high. Larger studies are needed for further evaluation of the technique and to define the future role of patient-specific template alignment techniques for TKA.