6-pyruvoyltetrahydropterin synthase (PTPS) deficiency is autosomal recessive disorder and the most common type of tetrahydrobiopterin (BH4) deficiency. It is caused by deficiency of PTPS, a cofactor involved in the biosynthesis of BH4 from guanosine triphosphate (GTP). Unlike classical phenylketonuria, which needs restriction of dietary phenylalanine for whole life, BH4 deficiency is treated by tetrahydrobiopterin, levodopa, and 5-hydroxytryptophan replacement. So it is important to make accurate diagnosis and initiate treatment as soon as possible for a better prognosis. There is no retrospective study of Korean patients undergoing long-term treatment for PTPS deficiency. We report 9 Korean patients with PTPS deficiency and their laboratory findings including BH4 loading tests, urine pterin tests, genotypes, dihydropteridine reductase (DHPR) activities and clinical manifestations including medication and developmental delay existence.