Encapsulation of the filtering bleb occurs as a complication of glaucoma filtering surgery in 8.3-28% of all eyes filtered, often between 2-4 weeks after surgery. It has a characteristic clinical appearance--highly elevated localized bleb, prominent surface vessels and patent sclerostomies on gonioscopy. This study retrospectively reviewed the results of 100 filtering operations, performed in the Prof. Dr. I. Stankovitsh Eye Department, focused on the incidence, possible risk factors and management of encapsulated filtering blebs. Trabeculectomy was done in all patients with limbus-based conjunctival flap, rectangular scleral flap 4 x 4 mm, and sclerostomy 2 x 2 mm. Two or three interrupted 10-0 nylon sutures were used to tether the flap, the conjunctiva with Tenon's capsule was closed with a running suture. All eyes received topical dexamethasone drops, mydriatics-homatropin or tropicamide and antibiotic ointment for three weeks. Possible risk factors were considered: sex, age, other eye or systemic disease, type of glaucoma, previous ocular procedure and antiglaucoma medical therapy, early postoperative complications, postoperative and final intraocular pressure (IOP). All eycs with encapsulated filtering bleb were given topical beta-blocker initially and carbonic anhydrase inhibitor, and if IOP continued to be uncontrolled incisional surgical management was performed. Success was defined as IOP maintained at less than 22 mmHg, with or without medication. An encapsulated filtering bleb developed in 9% of eyes. Previous argon laser trabeculoplasty was associated with an increased frequency of bleb encapsulation. The mean postoperative IOP was 11.30 +/- 1.90. Encapsulation of filtering bleb was developing at mean time of 19.9 +/- 3.0 after surgery. Six eyes returned to IOP below 21 (mean IOP was 20.17 +/- 0.90) within 4 weeks, and 4 of them continued on a topical beta-blocker. Four eyes required incisional surgery. A week after surgery mean IOP was 18 mmHg. Haemophthalmus occurred after one incision performed in a patient suffering from diabetes mellitus. Late scarring of the filtering bleb was developed in 2 eyes. Seven months and 2 years after filtration surgery mean IOP was 21.30 +/- 4.00 mmHg. The cause of bleb encapsulation is not known. Male patients, surgical glove powder, topical corticosteroids, previous argon laser trabeculoplasty and beta-blockers are some of potential risk factors for the development of encapsulated filtering bleb. This study suggests the association between development of encapsulated bleb and previous argon laser trabeculoplasty--40% in the eyes with encapsulation and 18% in the eyes without encapsulation. The optimal management of bleb encapsulation has not been defined. In this study topical antiglaucoma therapy achieved IOP control and cyst's remodeling in 60% of cases. Forty percent of all cysts required incisional surgical management. Encapsulation of the filtering bleb is not an uncommon complication of glaucoma filtration surgery. It is important to examine postoperative eyes frequently during the first 2 months to detect this complication. Fortunately, most eyes have their IOPs controlled with antiglaucoma therapy.