Pediatric patients with acute lymphoblastic leukemia (ALL) usually develop oral manifestations due to the disease itself, as well as side effects of chemotherapy that severely affect their health and quality of life. The aim of this paperis to determine the prevalence of oral diseases in pediatric all patients with and without chemotherapy and its relation to the different phases of chemotherapy. A cross-sectional observational study was conducted in 103 pediatric patients with all between 3-15 years. They were classified into groups: without chemotherapy and with chemotherapy at phase of consolidation, enhancement, maintenance and monitoring. Clinical diagnosis was performed and gingival inflammation index (IMPA) and caries criteria (dmf and DMF) were applied. The prevalence oral manifestations in the chemotherapy group were mucositis (98%), ulcers (90%), gingivitis (86%) and candidiasis (78%). The induction phase related with mucositis: RM = 7.6, 95%CI: 4.4-13, p = 0.0001; candidiasis: OR = 103, 95%CI: 13.0-818, p = 0.0001; gingivitis: OR = 16.2, 95%CI: 5.5-47, p = 0.0001; ulcers OR = 61.5, 95%CI: 8.7-432, p = 0.0001. The frequency and severity of oral diseases was hight and associated with the induction phase of chemotherapy, altering the overall nutrition and health of children.