The potential adverse effect of body mass index (BMI) on shoulder function scores after reverse shoulder arthroplasty (RSA) has not been investigated. We conducted a study to examine outcomes of RSA performed for rotator cuff tear arthropathy (RCTA) across BMI categories (normal weight, overweight, obese). We hypothesized that, compared with normal-weight patients, obese patients would have worse shoulder function scores, worse mobility, and more complications. Using a prospective shoulder arthroplasty registry, we identified 77 primary RSAs performed for RCTA with minimum 2-year follow-up. Thirty-four patients had normal weight (BMI <25 kg/m2), 21 were overweight (BMI 25-30 kg/m2), and 22 were obese (BMI >30 kg/m2). Shoulder function scores, mobility, and satisfaction were evaluated before surgery and at final follow-up. The 3 BMI groups were not significantly different on demographic factors, preoperative shoulder function scores, or preoperative mobility (P > .05). For each group, shoulder function scores and mobility significantly improved between the preoperative and final follow-up assessments (P < .001). Patient satisfaction was similar between groups (P = .967). Improved shoulder function scores, mobility, and patient satisfaction can be expected after RSA for RCTA in patients regardless of BMI.