Both surgical iridectomy and YAG-laser iridotomy have been shown to prevent angle-closure glaucoma. However, it remains unknown as to which procedure is superior. We therefore conducted a prospective randomized study, which compared the effect of the two methods on visual acuity, intraocular pressure, endothelial cell density, depth of the anterior chamber, and iris configuration as well as acceptance by the patients. A total of 30 patients, who were treated for acute angle-closure glaucoma in one eye, were subjected to either surgical iridectomy or Nd:YAG-laser iridotomy in the other eye according to a randomized protocol. All patients were followed for 12 months by examination at the 1st, 6th, and 12th month post treatment. No significant difference between the two treatments was found regarding visual acuity or intraocular pressure. The peripheral anterior chamber increased in depth following both methods, whereas the central depth of the anterior chamber was unaffected. A better gonioscopic visibility of the trabecular meshwork resulted from the increased width of the chamber angle. Whereas the number of endothelial cells remained constant in the patients treated with laser iridotomy, a small decrease was observed in the group of patients who underwent iridectomy (-7.2% after 12 months; difference not significant). The subjective acceptance by the patients was better in the group treated with laser iridotomy. We conclude that the two methods are equivalent with regard to intraocular pressure and visual acuity. The constant number of endothelial cells and the better acceptance by the patients suggest Nd:YAG-laser iridotomy to be the preferable method for prophylaxis of acute angle-closure glaucoma.