Of the filtering procedures employed, trabeculectomy is the one most frequently used for surgical therapy in primary open angle glaucoma patients. Intra- and postoperative complications must be detected promptly and treated adequately. Many complications arise within the first weeks, such as bleb scaring, decreased flow beneath the scleral flap, extensive filtration with choroidal detachment and anterior chamber narrowing. Fibrin reaction, corneal dellen, iris prolapse, conjunctival leakage and ciliary body detachment are seen more rarely. With prophylactic pre- and perioperative application of antibiotics, wound infections are rare and the risk of endophthalmitis following trabeculectomy remains small. Careful surgical planning requires special consideration of the conjunctiva and provides the basis for long-term success as long as intensive follow-up treatment is ensured. The success of trabeculectomy depends on the preoperative, intraoperative as well as postoperative condition and in particular on bleb development. Early detection of postoperative complications, especially in terms of early scaring in the bleb area, enables implementation of adequate therapeutic measures, such as needling procedures and early bleb revision. Close patient monitoring substantially increases long-term success rates.