Castro FG. Oral mucositis in pediatric patients undergoing hematopoietic cell transplantation [thesis]. São Paulo: Universidade de São Paulo, Faculdade de Odontologia; 2019. Versão Corrigida. Oral mucositis (OM) is one of the main morbidities in immediate periods after hematopoietic cell transplantation (HCT). In pediatric patients, OM is poorly described in the literature and there are no specific protocols for prevention and treatment of these lesions. The aim of this study was to characterize OM in pediatric patients before and during the periods after HCT, and also verify which patient and transplant-related factors may be associated with the duration and severity of these lesions. It was also analyzed the impact of OM on body mass changes, opioid prescription and artificial nutrition, as well as overall survival. For this, 115 medical records were selected from patients up to 18 years old, who underwent HCT, collecting information about the patient, transplantation and toxicity in gastrointestinal tract, from the conditioning period up to 10 days after the neutrophil engraftment. Patients were divided into age groups from 0 to 2, 3 to 6, 7 to 12, and 13 to 18 years old. There was a higher frequency of patients indicated to HCT due to primary immunodeficiencies (34.78%), followed by patients with hematologic malignancies (24.34%) and anemia (18.26%). There was a high frequency of patients from 0 to 2 years old (n=35 patients) and 7 to 12 years old (n=38). These patients were mainly submitted to allogeneic transplantation (87.93%) and conditioning containing bussulfan (57.40%). A higher frequency of OM grades 3 and 4 was observed in patients from 7 to 12 years old compared to other age groups (26.32%, p = 0.019). Longer duration of swallowing pain was also observed in this age group and in 13 to 18 years old group (p = 0.024). In general, at all ages, OM was not restricted to the neutropenia period, manifesting before or extending beyond that period. The prescription of artificial nutrition (71.30%) and opioids (84.16%) was high in all the sample. Patients from 0 to 2 years old needed artificial nutrition for longer period (p = 0.002). Prophylaxis for graft versus host disease (GVHD) with methotrexate was a significant risk factor for OM. Both OM grade 2 (OR = 12.6, p = 0.017) and duration of swallowing pain ³ 3 days (OR=6.5, p<0.001) significantly impacted opioid prescription. Swallowing pain also impacted the prescription of artificial nutrition (OR = 2.7, p = 0.018), but OM did not. None factors related to mucositis in the digestive tract was significantly associated with loss or gain of body mass, nor with overall survival. It was concluded that pediatric patients who underwent HCT exhibited different OM profiles according to age group, with variations in the period of manifestation severity and duration of these lesions. Specific oral care protocols for these age groups should be instituted, focusing mainly on the control of OM regarding to analgesia.