BACKGROUND: The management of acne remains a challenge, with current therapies linked to significant side effects and patient non-compliance. Phototherapy using blue light has been proven in the treatment of acne vulgaris and offers the clinician an effective alternative. OBJECTIVE: To determine the effect of narrowband light-emitting diode (LED) blue light in the reduction of inflammatory and non-inflammatory lesions in patients with mild to moderate acne and to evaluate patient tolerance of the therapy. METHODS: Forty-five patients were treated with high-intensity pure blue light, 415 nm and 48 J/cm2, receiving two treatments of 20 minutes per week for a period of 4-8 weeks. Clinical assessment was performed at baseline, and 2, 4 and 8 weeks after treatment. A patient's therapeutic response was measured using a global improvement scoring system. RESULTS: The mean improvement score was 3.14 at 4 weeks and 2.90 at 8 weeks. Nine patients experienced complete clearing at 8 weeks. The treatment was well tolerated, with 50% of patients highly satisfied with the treatment. CONCLUSION: This open-label study suggests the therapeutic efficacy of high-intensity LED pure blue light in the treatment of acne vulgaris with no reported side effects.