Background: Our aim was to determine the predictive value of postoperative bleb morphological features and intraocular pressure (IOP) on the success rate of trabeculectomy. Methods: In this prospective interventional case series, we analyzed for one year 80 consecutive primary open angle glaucoma patients who underwent mitomycin-augmented trabeculectomy. Bleb morphology was scored using the Indiana bleb appearance grading scale (IBAGS). Success was defined as IOP ≤15 mmHg with or without medications at 12 months. We tested for IOP and bleb morphological differences between groups, applied a multivariable regression analysis and determined the area under the receiver operating characteristic curve (AUC). Results: Age and gender were equally distributed (62.3±13.1 years, P=0.911). IOP of patients with a successful outcome did not differ from unsuccessful ones on day 1, 7 and 30 (all P≥0.2). The AUC of IOP at day 1, day 7 and 30 for predicting a successful outcome was 0.355, 0.452, and 0.80, respectively. The AUC for bleb morphology parameters, bleb height, extension, and vascularization, on day 14 were 0.368, 0.408, and 0.549, respectively. Values for day 30 were 0.428, 0.563, and 0.654. IOP change from day 1 to day 30 was a good predictor of failure (AUC=0.838, 95% CI: 0.704 to 0.971) with a change of more than 3 mmHg predicting failure with a sensitivity of 82.5% (95% CI: 68 to 91%) and a specificity of 87.5% (95% CI: 53 to 98%). Conclusions: The postoperative IOP on day 30 had a fair to good accuracy while the bleb features failed to predict a successful outcome. An IOP increase by as little as more than 3 mmHg during the first 30 days was a good predictor of failure.