Medium chain acyl CoA dehydrogenase deficiency (MCADD) is an uncommon inborn error of fatty acid oxidation that is a preventable cause of morbidity and mortality. Newborn screening for MCADD has been introduced in many centres worldwide and in this review we outline what the clinician needs to know. In most screening programmes a positive screening test has a high predictive value, but the diagnosis should always be confirmed independently. The basic treatment is dietary: avoid fasting and ensure a high carbohydrate intake during any illness. Careful attention to detail is essential as the long term outcome is only as good as the frontline clinical management.