Long-term efficacy of 360 degrees argon laser trabeculoplasty was studied in 118 eyes of 93 patients with uncontrolled chronic open-angle glaucoma. The mean intraocular pressure (IOP) decrease was 8.9 +/- 5.4 mmHg (mean +/- standard deviation [SD] in 71 eyes at 1 year, 9.3 +/- 4.3 mmHg (mean +/- SD) in 51 eyes at 3 years, and 10.3 +/- 3.9 mmHg (mean +/- SD) in 28 eyes at 5 years. The probability of success at 4 years (decrease in IOP greater than or equal to 3 mmHg, IOP less than or equal to 19 mmHg, stable visual field, stable optic nerve, and no further laser or surgical intervention) was 52%. Pretreatment IOP, diagnosis, previous operations, age, and sex were not significant determinants for success or failure. Eyes receiving argon laser trabeculoplasty before cataract surgery maintained control of IOP after surgery. Failure was most common in the first year after treatment (23%), and thereafter failure occurred at a rate of 7 to 10% per year.