Increased intraocular pressure (IOP) in encapsulated filtration blebs was evaluated in 49 eyes of 49 patients followed for 6 to 48 months (mean +/- standard deviation, 19.7 +/- 12.6 months). Intraocular pressure increased from 10.2 +/- 7.5 mmHg at 1 week postfiltration surgery to a peak of 26.1 +/- 10.7 mmHg at 3 weeks postoperatively and then decreased to 16.2 +/- 5.0 mmHg at 16 weeks and remained stable through the follow-up period. Thirty-nine eyes had a final IOP of 19 mmHg or less; 35 eyes required medical therapy alone (antiglaucoma drops, oral carbonic anhydrase inhibitors, and/or digital massage) with a final IOP of 14.1 +/- 3.8 mmHg; and 14 eyes required surgical reintervention for medically uncontrolled IOP elevation, and five of these eyes required two or more surgical reoperative procedures. Vigorous medical therapy, including glaucoma medications, topical steroids, and digital massage, is particularly important for encapsulated blebs during the first 2 months after surgery. After this period, IOP decreases and often remains sufficiently reduced to avoid further surgical intervention.