Background Head and neck radiotherapy is typically associated with toxicities that can have profound effects on the patient's quality of life. Xerostomia, which may or may not be related to hypofunction of the salivary gland, leading to negative consequences, mainly in quality of life, leaving patients more susceptible to the development of oral mucositis, dental caries, oral infection and difficulties in speech is one of the most common side effects of such treatment. The aim of the present study was to evaluate salivary function of patients in treatment with radiotherapy for head and neck cancer submitted to photobiomodulation. Material and Methods A cross-sectional study with a quantitative approach was carried out in the Dentistry Department of the Hospital de Câncer de Pernambuco between February and September 2019. Results The study sample comprised 23 patients of both genders, treated with radiotherapy for cancer in the head and neck region. The patients were submitted to photobiomodulation with infrared laser, as intraoral applications in order to prevent mucositis and extraoral applications to stimulate salivary glands. The applications were undertaken three times a week on alternate days throughout the radiotherapy period. The following parameters were used: Intraoral 15mW, 12J / cm2, 10s / point, 2.4 J / point, and extraoral 30mW, 7.5J / cm2, 10s / point, 0.3J / point, both with a wavelength of 830nm and area of 0.028cm². Subjective and objective symptoms were evaluated by measuring the unstimulated salivary flow (USF) using the spitting technique before, during and after radiotherapy treatment. For statistical analysis, a significance level of 5% was adopted. Most patients were male (70%) with 60 years of age on average. At the beginning of treatment, 22 patients had USF> 0.2 ml / min (grade 1), at the end of which 15 patients remained unchanged and only 3 patients progressed to grade 3. As for the subjective classification, most (52%) remained in grade 1 (absence of disability) throughout the treatment. Conclusions Based upon the results of this study it was possible to conclude that the use of photobiomodulation did not significantly interfere with the xerostomia complaint of patients in treatment with radiotherapy, however, it does seem to prevent patients from reaching higher degrees of xerostomia taking into account salivary flow measures. Key words: Photobiomodulation, head and neck neoplasms, radiotherapy, xerostomia, saliva.