A prospective short-term preliminary clinical study to evaluate the efficacy and immediate complications of Q-switched Nd-YAG laser iridotomy in the treatment of acute and chronic angle closure glaucoma is described. The follow-up period ranged from four to 10 months. Of 40 eyes treated 36 (90%) required a single lasing session for patency (19, one application; 17, two applications), and four eyes (10%) required two sessions. Closure of the iridotomy site following Nd-YAG lasing due to pigment epithelium proliferation occurred in 10% of eyes, an incidence remarkably lower than that of argon laser iridotomy. Transitory closure or diminution of a prior patent iridotomy during the first hour after lasing was observed in 6.7% of eyes. Patency was again noted up to three weeks later and remained unchanged. Immediate postoperative complications included a marked increase in ocular pressure (42% of eyes), minimal transitory bleeding, and transitory localised corneal oedema at the lasing site. Persistent iridocorneal adhesion at the lasing site was noted in three eyes, and localised lenticular opacities, of non-progressive type, were observed in one eye.