Serine deficiency disorders are rare defects in the biosynthesis of the amino acid L‐serine. At present two disorders have been reported: 3‐phosphoglycerate dehydrogenase deficiency and 3‐phosphoserine phosphatase deficiency. These enzyme defects lead to severe neurological symptoms such as congenital microcephaly and severe psychomotor retardation and in addition in patients with 3‐phosphoglycerate dehydrogenase deficiency to intractable seizures. These symptoms respond to a variable degree to treatment with L‐serine, sometimes combined with glycine. In this paper the current practice of amino acid treatment with L‐serine and glycine in serine deficiency is reviewed.