A 10-year-old pediatric patient diagnosed with cystic fibrosis was hospitalized due to an important clinical picture of acute primary herpetic gingivostomatitis (GEHA), with severe painful symptoms and difficulty in feeding orally. At the bedside evaluation and clinical examination, multiple ulcerated lesions were observed on the upper and lower lip, gingival ridge, and lingual dorsum, associated with pseudomembranous candidiasis on the tongue. We opted for the application of low-power laser daily, diet and hygiene guidance, and prescription of antiviral and antifungal drugs. Patient showed significant improvement on the third day of photobiomodulation associated with other care, with reintroduction of oral feeding and decreased use of analgesic therapy. Thus, understanding the complexity of viral infections associated with immunosuppression is important for making the correct diagnosis. The access to new technologies in dentistry improved the clinical condition of GEHA and the quality of life of the patient.