Pyruvate kinase (PK) deficiency is a common cause of hereditary non-spherocytic haemolytic anaemia. It is an autosomal recessive disorder caused by mutations in the gene coding for erythrocyte and liver-type pyruvate kinase (PKLR). So far, more than 130 mutations in this gene have been identified. Clinical symptoms, usually restricted to homozygous and compound-heterozygous individuals, are variable, ranging from neonatal jaundice requiring erythrocyte transfusions to a fully compensated haemolytic anaemia. The exact mechanism of erythrocyte destruction is unknown, however adenosine-triphosphate depletion and an increase in 2,3-disphosphoglycerate are thought to be important. The diagnosis of pyruvate kinase deficiency depends upon the demonstration of low PK enzyme activity. Due to the pitfalls in determining true PK activity, DNA testing is a valuable tool in the diagnosis of pyruvate kinase deficiency. By centralizing the molecular diagnostics of pyruvate kinase deficiency in Utrecht, more care can be provided for the diagnosis, treatment and support of patients.