Our case is a 16-year-old girl with methylmalonic acidaemia. She has progressive scoliosis which caused restrictive lung function impairment and therefore spinal surgery was contemplated. There was limited experience in operating these patients who are extremely vulnerabe in encountering stress. Anterior spinal fusion with instrumentation T11 to T14 was performed. Pre-operatively, sufficient glucose load was given during fasting. We closely monitored her blood gas, glucose, ammonia level, lactate, electrolytes and urine ketones. Intraoperatively, we avoided lactate containing intravenous fluid, N2O, NSAIDs and relaxants that are metabolized by ester hydrolysis. We used fresh blood for transfusions as old blood would give higher protein and acid load. TPN and carnitine infusions were started intraoperatively. Postoperatively, patient was transferred to PICU. Excellent pain control was given. Oral feeding was resumed as fast as patient could tolerate. We ensured that she has good bowel motion as gut bacteria can produce large amounts of propionic acid which is the direct precursor of MMA. Carbaglu and haemodialysis machine were arranged in case patient went into decompensation with hyperammonaemia. Conclusion: Patients with organic acidaemia can undergo major surgeries under general anaesthesia. However, detailed planning and cooperation among different disciplines are necessary for the success. A 37 years old female patient with classical MSUD was admitted to our hospital with a sore throat, anorexia, and decreased responsiveness. Her medical history contained psychomotor retardation, spastic tetraplegia and epilepsy as a result of dietary noncompliance in early childhood. A Candida stomatitis and dehydration were diagnosed. She was successfully rehydrated and treated with Fluconazole 200 mg orally for 10 days. After 4 days she was discharged in good condition. Metabolic laboratory results showed derangement of branched amino acids which was likely to be caused by an accidental switch of her amino acid mixtures to a urea cycle disorder preparation 21 days before admission. Although often thought of as a common complication, there is no peer reviewed publication regarding fungal infections during metabolic derangement in MSUD. Experiments in healthy rats show that an excess of dietary leucine can result in immune impairment as does a decreased BCKDH-activity in leucocytes and an increase of oxidative stress as seen in MSUD. Thus, immune impairment in MSUD derangement is comprehensible. Why fungal and not bacterial infections are prevalent in MSUD derangement, still remains to be elucidated.