To evaluate intraocular pressure (IOP) after phacoemulsification in patients with medically controlled open-angle glaucoma (OAG), and examine the association of biometric variables to IOP changes. Retrospective case series. Open-angle glaucoma patients without prior incisional glaucoma surgery undergoing phacoemulsification by a single surgeon between January 1997 and October 2011 were evaluated. Patient charts were reviewed to obtain demographic information, preoperative glaucoma medications, severity and treatment measures, and preoperative and postoperative IOP. A total of 157 eyes (157 patients) were included in the study. The average preoperative IOP of 16.3 ± 3.6 mm Hg decreased to 14.5 ± 3.4 mm Hg at 1 year (P < .001). Sixty eyes (38%) required additional medications or laser for IOP control within the first year postoperatively, or had a higher IOP at postoperative year 1 without medication change. Among eyes without postoperative medication changes (n = 102), higher preoperative IOP (P < .001), older age (P = .006), and deeper anterior chamber depth (P = .015) were associated with lower postoperative IOP. Phacoemulsification resulted in a small average decrease in IOP in patients with OAG. A sizeable proportion of medically controlled glaucoma patients with open angles undergoing phacoemulsification experienced an increase in IOP or required more aggressive treatment to control IOP postoperatively.