Phosphoglycerate kinase (PGK) deficiency is a rare X-linked disease that is characterised by mild to severe haemolytic anaemia, rhabdomyolysis, and variable defects in the central nervous system. In a white American family, two sons presented with haemolytic anaemia, seizures, and developmental delay. The diagnosis of PGK deficiency was made based on the remarkably low (<5% of normal) erythrocyte PGK enzyme activity level and the identification of a missense (c. 491A --> T) PGK1 gene mutation. This mutation results in an Asp164Val amino acid substitution, which has previously been designated PGK-Amiens and PGK-New York. The two new patients have the full clinical syndrome of PGK deficiency including haemolytic anaemia, developmental delay and seizures, and in the proband, hemiplegic migraines, retinal dystrophy and muscle fatigue. The PGK-Amiens/New York mutation had previously been found in a French patient and also in a large Chinese-Australian kindred, indicating that either the c. 91A --> T mutation is a recurrent mutation or that there is shared ancestry between the patients that have been identified so far with the mutation. Haplotype analysis of the c. 91A --> T mutation indicated that this was a recurrent mutation.