Thirty-seven eyes with open-angle glaucoma were treated by trabeculectomy and 34 eyes were treated by thermosclerostomy. Thermosclerostomy lowered intraocular pressure to a slightly greater extent than trabeculectomy; however, the average difference was not statistically significant except for the second year. After five years, IOPs were less than 22 mm Hg without additional medications or surgery in 24 (65%) of eyes undergoing trabeculectomy and in 14 (41%) of eyes undergoing thermosclerostomy. When eyes were included that were treated with medication or additional glaucoma or cataract surgery, over 90% of eyes in each group had an IOP less than 22 mm Hg. Visual acuity declined frequently in both groups, and progression of cataract was the most common cause. Loss of visual acuity occurred much more frequently in patients who were older than 60 years than in younger patients.