Purpose <p>To investigate, whether postoperative cystoid macular edema (CME) after combined XEN45 Gel Stent implantation with phacoemulsification has a predictive potential for the occurrence of bleb failure and subsequent conjunctival revision surgery.</p> Methods <p>This retrospective study involved 45 eyes of 45 participants being treated via combined XEN45 Gel Stent implantation with phacoemulsification and who received optical coherence tomography- (OCT) scans after surgery. In 15 eyes OCT detected a postoperative CME (CME group), the remaining 30 eyes did not show a postoperative CME (Control group). The occurrence of bleb failure and subsequent conjunctival revision surgery was compared among the two groups via a Kaplan-Meier survival analysis. A predictive potential was assessed via a Cox proportional hazards regression model. Postoperative intraocular pressure (IOP), medication scores, success and revision rates were compared.</p> Results <p>Bleb failure requiring conjunctival revision surgery occurred significantly more frequently in the CME group than in the Control group (87% vs. 50%, <i>p</i> = 0.039). The detection of CME went along with a 2.149-fold increased risk for bleb failure (<i>p</i> = 0.045). IOP decreased by 56% in the CME group, and by 42% in the Control group after an average follow-up of 32.9 ± 20.1 months and 24.8 ± 19.0 months, respectively. There was no significant difference in terms of postoperative IOP, medication scores and success rate observed.</p> Conclusions <p>Our results suggest that postoperative CME goes along with a considerably increased risk for bleb failure after combined XEN45 Gel Stent implantation with phacoemulsification. Therefore, when CME is detected postoperatively, close follow-up is advised.</p>