Purpose: To evaluate the intraocular pressure (IOP) response to selective laser trabeculoplasty (SLT) in the treatment of uncontrolled primary open-angle glaucoma (POAG) in a prospective clinical study. SLT is a new laser procedure that selectively targets trabecular meshwork (TM) cells without coagulative damage to the TM. Methods: 50 eyes with uncontrolled POAG were treated with a frequency-doubled, Q-switched Nd:YAG laser (532 nm). A total of approximately 50 nonoverlapping spots were placed over 180° of the TM at energy levels ranging from 0.40 to 0.92 mJ/pulse. After SLT, the eyes were maintained with the identical hypotensive medical therapy as that before treatment. IOP was estimated before and 1 day, 7 days, 1 month, 3 months and 6 months after treatment. Results: The mean pretreatment IOP was 22.48 mm Hg (SD 1.84). At the end of 1 month of follow-up IOP was reduced with a mean of 4.86 mm Hg (SD 2.38) or 21.6%; after 3 months, IOP was reduced with a mean of 5.66 mm Hg (SD 2.40) or 25.2%; at the end of 6 months of follow-up, IOP was reduced with a mean of 5.06 mm Hg (SD 2.37) or 22.5%. Conclusions: SLT is an effective method for lowering IOP in the treatment of POAG.