Este artigo está licenciado sob forma de uma licença Creative Commons Atribuição 4.0 Internacional, que permite uso irrestrito, distribuição e reprodução em qualquer meio, desde que a publicação original seja corretamente citada. ABSTRACT AIMS: To evaluate the effect of light emitting diode (LED) therapy on temporomandibular disorder. CASE DESCRIPTION: A woman diagnosed with temporomandibular disorder was subjected to four LED therapy sessions at a seven-day interval. In the initial examination of the temporomandibular joint the patient presented a mouth opening without pain of 23 mm, a maximum opening of 25 mm and a maximum opening with the aid of 27 mm. After the treatment, there was an increase of 7 mm in the opening without pain between the first and last evaluation, while the maximum opening of the mouth and the maximum opening with aid increased 6 mm between the first and last evaluation. After 21 days of treatment, a 50% reduction in painful sites was detected on the palpation examination.After the end of the treatment, the visual analog pain scale detected a decrease in pain intensity on both sides, and there was a decrease in the total mean pain intensity. By analyzing the responses to the Medical Outcomes Study 36-item Short Form Health Survey (SF-36), of the eight quality of life domains evaluated, four showed improvement. CONCLUSIONS: In this case study, after LED therapy there was reduction in pain intensity and increase of the mandibular range of motion. The resolution of the signs and symptoms of temporomandibular disorder resulted in patient's better quality of life.KEY WORDS: temporomandibular joint dysfunction syndrome; phototherapy; low-level light therapy.