Treatment of deformed type B glenoids with anatomical total shoulder arthroplasty (TSA) can be challenging when using standard imaging and instrumentation. 3D planning and PSI-guided (patient-specific instrumentation) eccentric reaming may substantially aid in both the glenoid correction and implantation of anatomical components in difficult cases. We hypothesized that the implementation of preoperative planning and a PSI-guided anatomical component protocol would result in accurate correction of the glenoid deformity and precise glenoid implant positioning. Twenty-two consecutive patients with primary glenohumeral osteoarthritis, intact rotator cuff and modified-Walch type B glenoids were treated with anatomical total shoulder arthroplasty. Preoperative 3D planning and PSI were used to guide eccentric reaming and correct glenoid deformity. Postoperative clinical and radiographic outcomes were assessed in all patients with a minimum follow-up of 2 years (mean of 26 months). Postoperative corrections of glenoid version and inclination were measured and the variation between preoperative planning and postoperative implant position was evaluated on CT 3D reconstructions. Similarly, both humeral subluxation in the axial scapular plane and glenoid joint line medialization were compared between preoperative and postoperative computed tomographic imaging. The mean age was 57 years (range, 54-68). Significant improvements in pain and functional outcome measurements were seen in all 22 subjects. Mean native glenoid version and inclination were −15° ± 5° and 3° ± 5°, respectively. Postoperatively, version was corrected to −7° ± 6° and inclination to 1° ± 2°. Cortical central peg perforation was noted in 1 case and cement perforation in 3 cases. The mean deviation from the preoperative plan was 3° ± 3° for version and 2° ± 2° for inclination. Humeral head subluxation improved from 68% ± 6% to 37% ± 6% and re-centering on the glenoid implant was achieved in all cases. The mean executed medialization of the glenoid joint line was 6 ± 3 mm and proved accurate to within 1 ± 1 mm of the planned medialization. A strong linear correlation was found between the degree of correction of retroversion and the amount of medialization (R = 0.82; P< .001). 3D preoperative planning and PSI guided correction of deformed modified-type B glenoids resulted in accurate postoperative correction of the glenoid deformity, correct glenoid component implantation with low deviation from the planned position and excellent short-term functional and radiographic results. : Level IV; Case Series; Treatment Study.