We investigated trabeculotomy ab externo as a means of optimizing intraocular pressure (IOP) control in glaucoma patients having phacoemulsification and implantation of an intraocular lens (IOL). A prospective, randomized, controlled study was performed to evaluate the effect on IOP and the incidence of complications associated with combined phacoemulsification and trabeculotomy ab externo. The study group had the combined procedure, while the control group had only phacoemulsification with IOL implantation. A total of 106 patients were randomized, and the IOP for each group was compared at 3, 6, 12, and 24 months. At two years, the mean IOP reduction was 6.1 mm Hg in the study group and 3.8 mm Hg in the control group (P = .001). There were no complications in the control group. Two complications (2/53 or 3.8%) occurred in the study group: a small tear in Descemet's membrane and a postoperative microhyphema. There was no increase in medication in either the study or control group. Combined phacoemulsification and trabeculotomy ab externo represents an option to lower IOP and potentially reduce the need for pressure-lowering medications in patients with primary open-angle glaucoma and visually significant cataracts.