OBJECTIVES: The objective of this paper was to characterize the population seen at the dentistry unit of the hematology-oncology service of the Oncology-Hematology Service, Instituto da Criança at the Hospital das Clínicas, Faculdade de Medicina, Universidade de São Paulo. Oral problems resulting from cancer therapy increase the risk of infection, length of hospital stay, treatment cost and negative impact on the course and prognosis of the disease. METHOD: Of the 367 medical records of cancer patients seen from November 2007 until December 2008: 186 with a cancer diagnosis and complete clinical data were selected, while 20 with a cancer diagnosis and incomplete records were excluded; 161 medical records with only hematological diagnosis were also excluded. The following characteristics were assessed: ethnicity, gender, age, diagnosis and characteristics of the neoplasm, cancer therapy status and performed dental procedures. RESULTS: Review of 1,236 visits indicated that 54% (n=100) of the patients had blood cancers, 46% (n=86) had solid tumors and 63% were undergoing anticancer therapy. The proportion of males (52.7%) in the study population was slightly greater. The most common cancer was acute lymphocytic leukemia (32.2%). Cancer occurred more often among those patients aged 5 to 9 years. The most common dental procedures were restorative treatment, preventive treatment and removal of infectious foci. CONCLUSION: The characteristics of the studied population were similar to those of the general Brazilian and global populations, especially regarding gender and diagnosis distributions. The aim of implementation of the dentistry unit was to maintain good oral health and patients' quality of life, which is critical to provide oral care and prevent future oral problems.