There are many types of cancers in children that are very different from those found in adults: leukaemia, lymphoma, and brain tumours are rather common in children. Acute lymphoblastic leukaemia (ALL) is the most common type of malignancy encountered. The role of pediatric dentist is very important before, during and after therapy: up to 24% of life-threatening infections arise from oral sites and areas. Early dental intervention and preventions procedures may significantly reduce oral complications associated with myelosuppressive cancer treatment. It is really important to evaluate the oral health surveys and to cut out potential sources of infection in mouth in these patients concurrent with their medical therapy. The aim of this review is summarizing the main features of oral mucositis in Childhood Acute Lymphoblastic Leukaemia, providing a little review for the approach, diagnosis and treatment of oral mucositis of ALL, which is frequent and potentially dangerous: it's important considering oral lesions of this type of childhood cancer in order to prevent complications before, during and after chemo or radio therapy to improve the quality of life of little patients.