Implant failure is a serious complication in reverse shoulder arthroplasty. We determined the incidence of glenosphere disengagement in a cohort of 479 reverse shoulder prostheses (468 Delta III™ [DePuy International Ltd, Leeds, UK], 11 Aequalis™ [Tornier, Grenoble, France]). We also determined whether disengagement adversely affected clinical outcomes. The minimum followup was 12 months (mean, 28.6 months; range, 12–72 months). Disengagement of the glenosphere occurred in 16 of 479 shoulders (3.2%). In 13 patients, the disengagement was partial (clear step-off between the baseplate and the glenosphere) and was not associated with a poor functional outcome with this short-term followup. In three patients, the disengagement led to a fracture of the central screw, leading to a complete disengagement of the glenosphere from the baseplate, necessitating revision in two; the third refused revision. Partial disengagement was seen in five of 11 Aequalis™ prostheses (45.4%) and eight of 468 Delta III™ prostheses (1.7%). The three total disengagements with central screw breakage all occurred in Delta III™ prostheses. We believe differences in the type of locking screws may explain the differences observed between the two types of reverse prostheses.