Argon laser iridotomy was performed in a total of 140 eyes of 104 patients with primary angle-closure glaucoma. A total of 69 eyes were treated by the long-burn technique and followed for an average period of 2.7 years; 71 eyes were treated by the short-burn technique and followed for an average period of 1.7 years. The effects on the IOP control and various factors of glaucoma were similar between both techniques, and the results of iridotomy were analyzed for all eyes. The IOP was controlled at or lower than 20 mmHg in 29% without medication, in 52% with reduced or the same medication as the preoperative treatments, and in 13% with increased medication. However, in 6% the IOP could not be controlled. The incidence of IOP control by iridotomy alone was significantly higher in eyes with peripheral anterior synechia (PAS) less than half the angle circumference than in eyes with more extensive PAS. Visual acuity loss occurred in 51%, and the loss by more than three lines of the acuity chart was seen in 19%; the visual loss was thought to be due to cataract progression or development. No significant differences were found in the visual field, cup-disk ratio, the extent of PAS or tonographic C-value before and after iridotomy. The IOP control and visual acuity loss were comparable with those seen after surgical iridectomy. Because of the absence of significant complications and ease of performance, iridotomy may replace surgical iridectomy in the treatment of angle-closure glaucoma.