Subthalamic osteotomy of the calcaneus is an original technique proposed by Pisani in 1981. Its two forms (addition and subtraction) are used to treat varus and valgus deformities. These are usually apparent in the frontal plane, and it is here that correction must take place. The first stage requires the execution of two osteotomy planes in an L shape; the first of these runs precalcaneocuboidally and is frontal, the second is subthalamic and incomplete to save the medial cortical layer: to be effective, its plane must be as horizontal as possible and at right angles to the axis of the leg. If addition is required, it is enough to force the posterior tuberosity in varus by separating the surfaces of the second osteotomy. The plane of the first osteotomy serves as the sliding surface, while the unimpaired medial cortical layer at the second serves as the hinge. The space thus created is used for insertion of a prismatic autoplastic bone transplant with an external base. If substraction is needed, a bone wedge with an external base and of the same shape is removed and the resection edges are then brought together. The spatial arrangement of the two osteotomy planes permits displacement into the frontal plane of the posterior tuberosity and most of the body of the calcaneus for the correction of either varism or valgism. The addition or subtraction wedge varies in degree to correspond with the real degree of correction. The path of the osteotomic lines does not interfere with the joint relations, particulary at the subtalar, i.e. the proximal element of the axial joint complex of the foot. Immobilisation is not required. Active kinesis in the immediate post-operative period is followed by loading after 30-50 days.