Glucose-6-phosphate dehydrogenase (G6PD) deficiency is the most common enzyme disorder. There are more than 400 million people worldwide with G6PD deficiency, and its distribution is similar to that of malaria. G6PD deficiency is an X-linked recessive disorder. Most patients with G6PD deficiency may be asymptomatic throughout their lives. They may present as neonatal jaundice, or acute and chronic hemolysis. The most important point in the management of G6PD deficiency is to avoid oxidative stress. The prevalence of G6PD deficiency in Korea is about 0.9%. However, a nationwide survey has revealed that the number of patients with enzymopathy is increasing. Immigration of different ethnicities into Korea, and the rise of interracial marriages will likely lead to an increase in the number of patients with G6PD deficiency.