The purpose of this study was to determine the prevalence of oral manifestations in pediatric patients with acute lymphoblastic leukemia (ALL) receiving chemotherapy, and to evaluate the significance of independent risk factors (oral health, gender, age, time and type of treatment, and phase of chemotherapy). A cross-sectional study was made in 49 children with ALL between 2 and 14 years of age. To describe oral manifestations, a clinical diagnosis was made and the following criteria were applied: the OHI-S index to describe oral health and the IMPA index to describe periodontal conditions and to differentiate gingivitis from periodontitis. The prevalence of oral manifestations was: gingivitis, 91.84%; caries, 81.63%; mucositis, 38.77%; periodontitis, 16.32%; cheilitis, 18.36%; recurrent herpes, 12.24%; and primary herpetic gingivostomatitis, 2.04%. Other oral manifestations were: dry lips, mucosal pallor, mucosal petechiae, ecchymoses, and induced ulcers. The prevalence of oral candidiasis was 6.12%. It was observed that high risk ALL and poor oral hygiene were important risk factors for the development of candidiasis and gingivitis. The type of leukemia, gender and phase of chemotherapy were apparently associated with the presence of candidiasis, gingivitis, and periodontitis, and they could be considered risk factors for the development of oral manifestations.