We investigate the refractive error after phacovitrectomy for rhegmatogenous retinal detachment (RRD; 100 eyes) and epiretinal membrane (ERM; 102 eyes). Axial lengths were measured by optical biometry in most patients. The main outcome measures were the refractive and absolute prediction errors. The overall mean refractive prediction error (ME) and mean absolute prediction error (MAE) were -0.40 ± 0.72 D and 0.62 ± 0.55 D, respectively, at 3 months postoperatively. The ME and MAE were significantly higher in the RRD group than in the ERM group (-0.63 ± 0.74 D vs -0.16 ± 0.63 D, P < 0.001 and 0.75 ± 0.62 D vs 0.49 ± 0.43 D, P = 0.002, respectively), indicating greater myopic shift in the RRD group. In the RRD group, adding +0.5 D to the preoperative predicted refractive power decreased the postoperative ME and MAE to -0.13 ± 0.74 D and 0.58 ± 0.47 D, respectively. Based on our results, we conclude that postoperative myopic shift was significantly higher in the RRD group than in the ERM group, possibly because of forward displacement of the intraocular lens by gas tamponade. The myopic shift can be minimized by adding +0.5 D to the predicted refractive power in patients undergoing phacovitrectomy for RRD.