Vincristine (VCR) as a key drug for the treatment of acute lymphoblastic leukemia (ALL) is associated with neurotoxicity. We present a young man with a history of controlled childhood seizures who was diagnosed with pre-B-cell ALL and developed generalized tonic-clonic seizures following the Cancer and Leukemia Group B (CALGB) 8811 regimen. The patient also received oral itraconazole to prevent fungal infection initiated by chemotherapy. Possible causes of seizure, including electrolyte abnormalities, hypoglycemia, central nervous system infection or inflammation, were ruled out. According to the Naranjo Adverse Drug Reaction Scale, the patient's seizure had been attributed to VCR, possibly secondary to concomitant use of itraconazole and doxorubicin. The patient successfully recovered after discontinuation of VCR and supportive care. Clinicians should be aware of the possibility of vincristine-induced seizure in adult patients, especially with the concomitant use of drugs known to have potential drug-drug interactions.