OBJECTIVE Argon laser trabeculoplasty (ALT) is commonly used in the treatment of open-angle glaucoma. Varying success rates in lowering intraocular pressure (IOP) and controlling glaucoma are reported in studies with follow-up periods from 1 to 5 years, and few reports are available with follow-up to 10 years. The authors retrospectively reviewed the efficacy of ALT in patients followed up to 10 years. METHODS Ninety-three patients with open-angle glaucoma underwent 360 degrees ALT. Mean follow-up was 52 +/- 43 months (mean +/- standard deviation; range, 1-132 months). Successful treatment at the time of final follow-up was defined as a decrease in IOP of 3 mmHg or greater from pretreatment level, IOP of 19 mmHg or less, stable visual field, stable optic nerve, and no further laser or surgical intervention. RESULTS The decrease in IOP was 8.9 +/- 5.4 mmHg at 1 year, 10.0 +/- 4.2 mmHg at 5 years, and 8.9 +/- 5.2 mmHg at 10 years. The probability of success at 1 year was 77%, at 5 years 49%, and at 10 years 32%. Failure was most common in the first year after treatment (23%), and thereafter failure occurred at a rate of 5% to 9% per year. The mean decrease in IOP for all 93 eyes at time of maximum follow-up was 6.1 +/- 7.1 mmHg. CONCLUSIONS Argon laser trabeculoplasty is an effective means for reducing IOP in many patients followed for an extended time. However, up to one half of eyes within 5 years of ALT and two thirds of eyes within 10 years may require additional laser or surgical intervention for glaucoma control.