The efficacy of nonablative fractional laser resurfacing of acne scars has been described in case reports and uncontrolled trials. The present study is the first randomized controlled trial in this field. The aim of this study was to examine the efficacy and adverse effects of 1,540-nm nonablative fractional laser treatment of acne scars. Ten patients with acne scars were included. Two intraindividual areas of similar size and appearance within contralateral anatomical regions were randomized to (1) 3-monthly laser treatments with a StarLux 1,540-nm fractional handpiece, and (2) no treatment. Blinded on-site clinical evaluations were performed before treatment, and at 4 and 12 weeks after the final treatment. End-points were overall change in scar texture (from score 0, even texture, to 10, worst possible scarring), adverse effects, change in skin colour (from score 0, absent, to 10, worst possible), and patient satisfaction (from score 0, no satisfaction, to 10, best imaginable satisfaction). Before treatment, scars were moderately atrophic and uneven in texture on both treated and untreated sides (median score 6.5, interquartile range 4.5-8; P=1). After treatment, laser-treated scars appeared more even and smooth than untreated control areas (4.5, 2-6.5, versus 6.5, 4.5-8, P=0.0156, at 4 weeks; 4.5, 2.5-6.5, versus 6.5, 4.5-8, at 12 weeks; P=0.0313). Patients were satisfied with the treatment (5.5, 1-7, after 12 weeks) and five of the ten patients evaluated their acne scars as moderately or significantly improved. No differences were found in skin redness or pigmentation between before and after treatment. Patients experienced moderate pain, erythema, oedema, bullae, and crusts. No adverse effects were seen in untreated control areas. The nonablative 1,540-nm fractional laser improves acne scars with a minimum of adverse effects.