Tumors of the oral cavity are of various origins and can be signs of non-invasive cysts or malignant neoplasms.The paper describes the case of a 9-year-old boy with a tumor in the right side of the maxilla. Having been treated for an odontogenic myxoma at the age of 3, the patient was included in a national program assessing the health of children who had undergone anticancer treatment. The boy remained under oncological supervision, and the tumor was found again in the same region a few years later. It was diagnosed as a dentigerous cyst and surgically excised. In addition, when the patient was 9 several changes in dentition were found that were typical following anticancer therapy: no tooth germs were observed for teeth 13, 35 and 45, and microdontic teeth 25 and 47 were noted. These changes could be attributed to the chemotherapy performed in early childhood. Tumors appearing in the oral cavity always require an in-depth assessment of their nature and origin. Chemotherapy elicits late complications in tooth development in children.