YAG laser treatment was used in 22 consecutive cases of failed or failing trabeculectomy. Seven treatments were considered to be successful with a mean decrease in intraocular pressure of 9.8 mm Hg (6 to 13 mm Hg) over a mean follow-up period of 10.7 months (two to 18 months). In the successful cases the trabeculectomy was the first intraocular surgery that the eye had undergone and the average time from trabeculectomy to YAG laser treatment was relatively short, 6.7 weeks, compared to 1.1 years for the failures. The major complication was an increase in intraocular pressure of 4 mm Hg or more in nine (60%) of the failed cases two hours after laser treatment.