Introduction and Background The purpose of this study was to evaluate the influence of different magnitudes of medialization of the bone-baseplate interface (MBBI) on clinical outcomes including range of motion (ROM), patient reported outcomes (PROs) and incidence of baseplate failure and scapula notching. Material and Method We retrospectively reviewed 91 patients who underwent primary RSA after a minimum 2-year follow-up. The amount of MBBI was estimated using a 3D CT-based computer planning software (Figure 1). Patients were categorized into three groups depending on whether MBBI was less than 3 mm (Group low MBBI, N = 32), between 3 mm to 5 mm (Group moderate MBBI, N = 30), or more than 5 mm (Group high MBBI, N = 29). Range of motion (ROM), ASES score, SST score, and scapular notching were compared between groups. Results Mean MBBI was 1.5 mm (range, 0.5 - 2.5 mm) in low MBBI group, 3.5 mm (range, 3.0 - 5.0 mm) in moderate MBBI group, and 7 mm (range, 5.5 – 10.0 mm) in high MBBI group. At the last follow-up, all patients demonstrated significant improvements in the ROM and functional scores without significant differences in the mean improvement between the three groups (Table 1). There was no correlation between the amount of MBBI and improvement in ROM in any plane. There was no statistical difference (P > 0.05) in the incidence of baseplate failure and scapula notching at the final follow up in low MBBI (17%), moderate MBBI (33%), and high MBBI group (24%). Conclusions This study found that, in primary RSA using a lateralized implant, medialization of glenoid bone-baseplate interface after eccentric reaming does not influence shoulder ROM, PROs, baseplate loosening, or glenoid notching. Further studies with more accurate measuring techniques of MBBI and its results upon patient, implant, and surgical variables are warranted.