Purpose: To evaluate the long-term efficacy of Selective Laser Trabeculoplasty (SLT) in patients with first diagnosed and advanced primary open angle glaucoma (POAG). Methods: This study is a retrospective chart review of patients with OHT, first diagnosed early POAG without any medication and uncontrolled POAG with maximum tolerated medical therapy who underwent SLT at the Sifa University, between July 2010 and July 2011.The aforementioned data were gathered from the, 3-month, 6-month, 12-month, 24-month, and 36-month postoperative visits. Both groups were compared regarding decrease in IOP, percentage of IOP decrease, and success rate after SLT treatment. The data were analyzed using independent t-test to compare IOP levels and the decrease of IOP between the both groups at different time points. A P-Value of P<0.05 was considered as statistically significant. Results: The mean IOP in the 3 groups at baseline was similar and did not reach statistical significance. The therapy effect was stronger in the early POAG patients in the first year. The success rate at the last visit at 36th month was 44.4% in the group of first diagnosed POAG, and 23.5% in the group of uncontrolled POAG. Conclusion: The long-term therapeutic effect in patients with OHT and first diagnosed POAG is moderate. The efficacy is lesser in advanced patients. However, the main advantage of SLT is the protecting of the ocular surface from the toxicity of the preservants of anti-glaucoma drops.