Objective: This study aimed to appraise the efficacy of a 577 nm high-power optically pumped semiconductor laser (HOPSL) for the treatment of inflammatory acne.Methods: The study included 50 patients with acne vulgaris (inflammatory type), 14 men, and 36 females; patient ages ranged from 16 to 35 years. The left side of the face was treated with a single pass of a 577 nm high-power optically pumped semiconductor laser every 2 weeks for 3 sessions. Patients were examined prior to the first session and 4 weeks after the last session (Investigator's Global Assessment of acne severity, IGA; single lesion count).Results: At baseline, no statistically significant difference in the severity of inflammatory acne lesions between both sides was observed. One month after the final session, a significant improvement (IGA reduction of >50 percent) of the over-all severity of the acne was observed in 49 patients (98 percent) on laser-treated side versus 41 (82 percent) the control side of the face (P < .05). Accordingly, we found a significant reduction in the mean percentage of inflammatory papules, pustules, and nodules (79.33 vs 56.92, 78.04 vs 43.33, 64.85 vs 21.93 percent, respectively) (P<0.05). Side effects in the form of erythema and irritation during sessions were transient and tolerated by the patients.Conclusion: The 577 nm high-power optically pumped semiconductor laser is effective and safe for the treatment of inflammatory lesions (papules, pustules, and nodules) in acne patients.Running title: 577 nm high-power optically pumped semiconductor laser (HOPSL) for the treatment of inflammatory acne