Forty eyes in 37 patients that had previously successful 360 degrees argon laser trabeculoplasty were again found to have uncontrolled intraocular pressure (IOP) on maximally tolerated medical therapy and were retreated with argon laser trabeculoplasty to 180 degrees of the trabecular circumference. Successful retreatment was considered a decrease in IOP of 3 mmHg or more and sufficient to avoid further laser therapy or invasive glaucoma surgery. Laser trabeculoplasty retreatment was successful in 13 of the eyes treated (32%). Retreatment failed to control IOP in 27 of the retreated eyes (68%): either the IOP was not lowered by at least 3 mmHg (4 eyes) or the eyes required further laser therapy or surgery (23 eyes). The probability of successful IOP control 1 year after retreatment was 33% and only 14% after 1.75 years. No IOP elevations greater than 6 mmHg were recognized in the postlaser period. Although retreatment with argon laser trabeculoplasty can safely be used to control the IOP in some glaucomatous eyes, the likelihood of success is low.