Background: PWS is a vascular malformation presented at birth and associated with a psychological problem to the patients. Many types of laser systems were used to solve this problem. Aim of the study: To assess the efficacy of long-pulsed Nd:YAG 532-nm laser in the treatment of port wine stain both clinically and by imaging technique. Patients and methods: This is an interventional therapeutic clinical study for the treatment of facial port-twine stain with long-pulsed, 532-nm, Nd:YAG laser. The treatment sessions were done every 4 weeks for 12 sessions and follow-up after 3 months of the last session. The assessment of the response was done before and at the end of follow-up period, both objectively (percent of improvement, photo comparison by using PSNR) and subjectively (patient satisfaction). Results: Sixteen patients completed all sessions of the treatment. The improvement score for the PWS were failure = 0%, mild = 6.25%, moderate = 12.5%, good = 31.25%, and excellent = 50%. The values of PSNR for all the patients have been recorded and were fewer than 25 which means that the response for the treated lesions was very good. Conclusion: The long-pulsed Nd:YAG laser 532 nm is an effective and safe method of treatment of facial PWSs without significant residue. The PSNR was a new, simple, cheap and noninvasive method for assessment of the response of PWSs to laser therapy.