Phacoemulsification-aspiration and intraocular lens implantation (PEA + IOL) were carried out in 40 primary open angle glaucoma (POAG) eyes without history of surgery and 53 control (cataract only) eyes. Postoperative change in intraocular pressure (IOP) was evaluated over a long period (at least 18 months, average follow-up period 34 months). The postoperative IOP was significantly lower than the preoperative level in every group from 6 months to 3 years. An IOP decrease of 1.5 mmHg was maintained for 3 years in the control group. A decrease of 2.5 mmHg was stable for 3 years in the good POAG group in which preoperative IOP was controlled (< or = 20 mmHg) with medication. IOP decrease in the poor POAG group in which preoperative IOP was over 21 mmHg with medication, was 5.5 mmHg, and was maintained for 3 years. Medication did not differ significantly before or after the operation. These results imply that in POAG an IOP decrease can be expected after PEA + IOL.