To investigate low-level laser therapy (LLLT) applied to treat burning mouth syndrome (BMS). This prospective, comparative, partially blinded, single-centre, clinical trial of GaAlAs Laser, with 815 nm wavelength, included 44 BMS patients divided randomly into three groups: Group I (n = 16): GaAlAs laser 815 nm wavelength, 1 W output power, continuous emissions, 4 s, 4 J and fluence rate 133·3 J cm ; Group II (n = 16): GaAlAs infrared laser, 815 nm wavelength, 1 W output power, continuous emissions, 6 s, 6 J and fluence rate 200 J cm ; Group III (n = 12) placebo group, sham laser. All groups received a weekly dose for 4 weeks. Pain intensity was recorded using a 10-cm visual analogue scale; patients responded to the oral health impact profile (OHIP-14), xerostomia severity test and the hospital anxiety-depression scale (HAD). These assessments were performed at baseline, 2 and 4 weeks. LLLT decreased pain intensity and improved OHIP-14 scores significantly from baseline to 2 weeks in groups I and II compared with the placebo group. No statistically significant differences were found from 2 to 4 weeks. Overall improvements in visual analogue scale (VAS) scores from baseline to the end of treatment were as follows: Group I 15·7%; Group II 15·6%; Group III placebo 7·3%. LLLT application reduces symptoms slightly in BMS patients.