Leukemias are neoplastic diseases originating from the hematopoietic system and may be generally divided into acute and chronic forms. Dental treatment of patients with leukemia should be planned on the basis of antineoplastic therapy, which can be chemotherapy with or without radiotherapy and bone marrow transplantation. This is an orginal study with a sample of 102 adolescents evaluated before and after chemotherapy. Within oral mucosa of the examined patients ulcerations and gingival hyperplasia were the most frequently observed. These are typical disorders of the oral mucosa that occur in leukemia. The decrease in the number of red blood cells and hemoglobin predisposes to pathological changes within the oral mucosa. Pathological changes within the oral mucosa were also observed more often in patients after chemotherapy who had decreased immunity assessed on the basis of a white blood cell count. It is concluded in this paper that dental treatment in relation to hematological indices presented by patients with leukemia must follow certain protocols, mainly related to white and red blood cells or platelet counts, and the presence of the dentist in a multidisciplinary team is required for the health care of such patients. Lukemic patients require permanent dental control. It can mitigate pathological processes in the oral cavity related to the disease and its treatment. Such an approach will help prevent local complications also affecting patients’ general condition.