Acute lymphoblastic leukemia is a common malignancy in childhood. Managing adverse events during treatment can result in very complex situations. A previously healthy adolescent diagnosed with T-cell acute lymphoblastic leukemia developed on day +55 of induction chemotherapy hemiparesis, dysesthesia, and facial palsy. Blood tests and brain imaging techniques were unremarkable. The patient was diagnosed with a conversion disorder, which completely resolved. Although rare in clinical practice, children and adolescents with cancer do not always have organic pathology explaining their symptoms. Psychiatric disorders such as those of the somatoform spectrum must be considered, particularly in patients with anxiety or depression.