Substantial posterior glenoid wear causing static posterior subluxation of the humeral head in patients with primary osteoarthritis has been described. Persistent humeral head subluxation after total shoulder arthroplasty can result in early polyethylene wear and glenoid component loosening. In our prospective cohort study, we hypothesized that in patients with posterior glenoid wear from osteoarthritis, static posterior decentering of the humeral head could be recentered during total shoulder arthroplasty by surgical correction of glenoid alignment in the transverse plane with soft tissue balancing. We performed total shoulder arthroplasties in 77 patients with primary osteoarthritis and a mean age of 67.6 years. The mean clinical and radiographic followup was 2 years (range, 1-7 years). Patients with preoperative posteriorly decentered humeral heads did not have posterior decentering develop postoperatively. Twenty patients (83.3%) had centered humeral heads and four patients (16.6%) had anterior decentering. Midterm results of total shoulder arthroplasties in shoulders with humeral head decentering caused by glenoid deficiency in the transverse plane showed correction of the decentering by lowering the high side or by bone grafting with soft tissue balancing can be well maintained.