PURPOSE: To investigate the incidence and course of encapsulated filtering blebs (EB) following primary standard trabeculectomy in eyes with non-complicated glaucoma. MATERIALS AND METHODS: Records of patients who were being followed-up in Ankara Numune Hospital, 1st Eye Clinic Glaucoma Department were analyzed and 183 eyes of 183 consecutive patients who underwent primary trabeculectomy without antimetabolites were enrolled in the study. RESULTS: Encapsulation developed in 14 (7.6%) of 183 eyes and identification of bleb encapsulation occurred at a mean follow-up time of 5.1 +/- 5.0 weeks (median = 4 weeks). Mean intraocular pressure (IOP) levels before, during, and after the encapsulated bleb phase were 14.1 +/- 3.6, 23.4 +/- 6.9, and 14.4 +/- 3.9 mm Hg respectively. All eyes responded to conservative medical treatment consisting of aqueous suppressants without digital massage, and encapsulation resolved after a mean duration of 8.3 +/- 4.6 weeks (median = 8 weeks). Patient age, gender, glaucoma diagnosis, and preoperative IOP levels were not significantly related with the occurrence of EB formation. There was no significant difference in the use of topical beta-blockers and miotics in patients that developed EB versus those who did not; however, EB developed only in eyes with prior beta-blocker therapy and no encapsulation occurred in the 16 eyes that had not received topical beta-blockers. Mean duration of follow-up was 45.3 +/- 30.7 months (12 to 127 months) in the group without encapsulation and 44.6 +/- 22.7 months (18 to 84 months) in the EB group. Overall success rates of trabeculectomies in eyes with and without EB were not significantly different (100% and 91.7%, respectively). Complete surgical success, however, without antiglaucomatous medications at the last visit was significantly lower in eyes with prior encapsulation (35.7% with EB, 63.9% without EB) (P = 0.014). CONCLUSION: Filtering bleb encapsulation following primary trabeculectomy responds well to conservative medical IOP-lowering therapy in eyes with glaucoma associated with elevated IOP.