SummaryPyruvate dehydrogenase (PDH) deficiency has long been recognized as the most common defined cause of primary lactic acidosis in infancy and early childhood. More recently, it has also been described in patients with subacute/chronic neurodegenerative disease without significant metabolic acidosis. The great majority of cases of PDH deficiency result from a genetic defect in the E1α subunit of the complex. PDH E1α deficiency is an X‐linked inborn error of metabolism in which a high proportion of heterozygous females manifest the condition. In this review of 29 patients with PDH E1α deficiency, particular emphasis is given to those aspects of the disorder which are specifically related to the X chromosome location of the PDH E1α gene. These include the broad spectrum of clinical presentations and problems of diagnosis, especially antenatal diagnosis, in females.