Opening wedge osteotomy has recently gained popularity, thanks to the recent implementation of locking plates, which have shown equivalent stability with greater reproducibility, accuracy, and longevity than the closing wedge techniques and a lower prosthetic conversion rate. We present a new "do-it-yourself" cutting guides system for tibial opening osteotomy. Using a conventional computed tomography digital image, a positioning guide and wedge spacers were printed in three dimensions (3D) for implementing the osteotomy and obtaining the planned correction. The surgeon makes the whole process in a do-it-yourself style. This new technique was used in eight cases. Previous opening osteotomies with the standard technique were used as control (20 cases). Surgical time, fluoroscopic time, and accuracy of the axial correction were measured. The use of a custom positioning guide reduced the surgical (31 minutes less) and fluoroscopic times (6.9 times less) while achieving a high-axis correction accuracy compared with the standard technique. Digitally planned and executed osteotomies under 3D printed osteotomy positioning guides help the surgeon to minimize human error while reducing surgical time. The reproducibility of this technique is very robust, allowing a transfer of the steps planned in a virtual environment to the operating table.