Objective: Cytosine Arabinoside (cytarabine, ARA-C) discovered in the early 1950s from crptathetia crpta which is a type of sponge. It is a chemotherapeutic agent that is an analogue of primidine from the group of antimetabolites and it is used in AML (acute myeloid leukemia), ALL (acute lymphoblastic leukemia), CML (chronic myeloid leukemia), relapse or refractory hodgkin lymphoma, non-hodgkin lymphoma, primary central nervous system lymphoma treatment. The most common side effect is cytopenias due to the bone marrow suppression. In addition; side effects may occur such as nausea, vomiting, diarrhea, abdominal pain, hepatic dysfunction, neurological side effects. Beside many neurological side effects such as peripheral neuropaty, convulsion, cerebral dysfunction can be seen in systemic and intrathecal treatments, classical cytarabine neurotoxicity is acute cerebellar syndrome caused by high-dose systemic therapy.

Case report: A 61 year-old man who had lung cancer history and not suitable for allogeneic stem cell transplantation; was planned HyperCVAD A/B chemotherapy protocol with the diagnosis of B-ALL. Dysarthria and impaired coordination of hand and foot movements occurred on the sixth days of second cycle of HyperCVAD-B chemotherapy. In neurologic examination, dysarthric speech, measured and sequential motion tests for cerebral examination was failed and no motor deficits. No mass or vascular pathology were detected in imaging examinations that could explain the patient's complaint. As a result, the patient was evaluated acute cerebellar syndrome caused by high dose cytosine arabinoside side effect by neurology department. From the eleventh day of treatment patient's complaints was regressed and come back to normal at fifteenth days of treatment.

Conclusion: Acute cerebellar syndrome begins 3–8 days after the start of drug administration. Cerebellar symptoms such as dysarthria, dysdiadokokinesia, dysmetry and ataxia greatly improved after stopping the drug however these symptoms may not full recover in approximately 1/3 of patients. Therefore there is not any treatment for neurological side effects, it should be kept in mind in chemoterapy treatment planning. While planning treatment, dose adjustment considering side effects as performance and age of patient. Nearly monitored is most important for early diagnosed of neurological symptoms.