Prospective evaluation of the buccal mucosa of pediatric patients with acute lymphocytic leukemia (ALL) regarding its clinical aspect and expression of members from the HHV family. Methods: From September 2014 to January 2015, a series of nine consecutive patients was evaluated, with ages ranging from 2 to 14 years, in treatment at the Amazon Hematology and Hemotherapy Foundation (HEMOAM). The buccal mucosa of those patients was clinically evaluated, screened for alterations and analyzed by PCR, to search DNA from HSV-1, CMV and EBV during four moments of the pre-phase/induction phase of the chemotherapy treatment (P/I)-D0/D1, D8, D15 and D35, as well as four moments of the consolidation of the remission phase (CR)-D1, D15, D29 and D50. The protocol proposed by the Brazilian Cooperative Group for Treatment of Childhood Lymphocytic Leukemia (GBTLI ALL-2009) was followed. Results: A prevalence of 2-year-old children (66.7%, n=6) with a diagnose of B-cell ALL (88.9%, n=8) was observed. Buccal alterations were observed in 33.3% (n=3) of the patients: erythema (D35 P/I), dry lips (D8 and D15 P/I) and an episode of xerostomia (D15 P/I). None of the samples was positive for HSV-1 and CMV, but 33.3% (n=3) of the cases expressed EBV (D8 and D15 P/I). Conclusions: Buccal alterations and the presence of HSV-1, CMV and EBV in patients with ALL was inexpressive, with most of the patients being sound throughout the treatment. Thus, it cannot be affirmed that the analyzed viruses are part of the microbiome of those patients. However, it has been suggested that the presence of EBV is more expected than