Objective: This study presented the infants born with twin pregnancy who were suffering from congenital leukemia. One of them, 9 weeks old boy, was accidentally administrated intrathecal injection of vincristine. The mistake was noticed immediately. The cerebrospinal fluid was removed with the given medications. Next lavage of spinal cord by Solutio Ringeri Lactate with FFP, were included and the intravenous cytoprotective treatment was used. Neurologic symptoms appeared after 5 days. The patient died after 115 days of hospitalization. The causes of fateful mistake was analysed, found the recommendations and changed interdisciplinary working procedures in the hospital. Conclusions: Intrathecal injection of vincristine, led to death of the infant, despite the inclusion of multiple treatment.