This article presents the results of using a simple closed screening questionnaire for oncopediatricians to identify mental disorders in children and adolescents with cancer. Long-term experience of monitoring underage patients suffering from cancer suggests that borderline mental disorders are widespread among these patients. Their diagnosis and therapy, which go beyond traditional specialized cancer care, require practitioners to have appropriate qualifications, which many pediatric oncologists do not have. To facilitate the selection of patients who need to consult a psychiatrist, oncopediatriciansare offered a simple screening questionnaire, which takes a minimum of time to complete, and which can be easily used when examining all patients under treatment.