Objective: Methylene tetrahydrofolate reductase (MTHFR) deficiency is an autosomal recessive disorder that results in increased homocysteine levels in the body. Hyperhomocysteinemia causes a predisposition to venous and arterial thrombosis and ischaemic insults. The incidence of the deficiency is around 40% in some countries. In this study, we aimed to evaluate the effects of anaesthetic agents in children with MTHFR deficiency. Methods:Twelve paediatric patients with an MTHFR enzyme deficiency who underwent surgery in a ten-month period in a single centre were retrospectively evaluated. Demographic data, homocysteine levels before and after surgery, anaesthesia management and postoperative complications were recorded. Results:In four patients, propofol was used both for anaesthesia induction and total intravenous anaesthesia (TIVA). Eight patients received sevoflurane for both induction and maintenance of anaesthesia. Nitrous oxide (N 2 O) was not used in any patients.There was not a significant difference between the preoperative and postoperative homocysteine levels (p>0.05). Twenty-four hours after the surgery, the homocysteine levels were within normal limits. No complications were observed. Conclusion:Sevoflurane and propofol have no deleterious effects on homocysteine levels in patients with MTHFR deficiency. Avoidance of N 2 O is the key point for anaesthetic consideration regarding these patients.