The COVID-19 outbreak has caused anxiety among children with hematology-oncology disease and their families, as it has in every segment of society. In this study, we aimed to detect the anxiety levels of children with hematologic or oncologic disease and of their parents after the COVID-19 outbreak. The sample consisted of 15 patients 12 to 18 years of age receiving treatment in the Pediatric Hematology and Oncology Unit in Altinbas University Medical Faculty Bahcelievler Medikalpark Hospital and 33 parents of the same unit patients between 6 and 18 years of age, and their 35 healthy peers and their parents. The State-Trait Anxiety Inventory was applied to participant children and their parents to evaluate their general anxiety and pandemic-related anxiety levels. Children with a hematology-oncology disease and their families were compared with healthy peers and their families. No significant difference was observed for pandemic-related anxiety levels (P>0.05). Both parent groups exhibited higher anxiety levels with regard to the pandemic than did their children (P<0.05). Children with hematology-oncology disease reported significantly higher trait anxiety levels when compared with healthy peers (P=0.01). The families of children who had not received stem cell transplantation had higher state and trait anxiety scores than the families of children who had received the transplantation (P<0.05). Even though they were in the high-risk group, children with a hematology-oncology disease and their families had pandemic-related anxiety levels comparable with those of healthy peers and their families.