Sarcosinaemia is a metabolic disorder characterised by an increased concentration of sarcosine in plasma and urine due to sarcosine dehydrogenase deficiency. Prevalence has been estimated at 1:28,000 to 1:350,000 in newborn screening programs. Sarcosinaemia is most probably a benign condition without significant clinical problems. It is transmitted in an autosomal recessive manner. Mutations in the gene for sarcosine dehydrogenase, located on chromosome 9q34, have been associated with this deficiency.