In the past 10 years, we have diagnosed congenital hemolytic anemia in 294 patients, approximately 33% of whom were found to have glucose-6-phosphate dehydrogenase (G6PD) deficiency. It is becoming more common for Japanese to marry people of other ethnic origins, such that G6PD deficiency is becoming more prevalent in Japan. Japanese G6PD deficiency tends to be diagnosed in the neonatal period due to severe jaundice, while G6PD-deficient patients with foreign ancestors tend to be diagnosed at the onset of an acute hemolytic crisis before the age of six. It is difficult to predict the clinical course of each patient by G6PD activity, reduced glutathione content, or the presence/absence of severe neonatal jaundice. We propose that both neonatal G6PD screening and systematic analyses of G6PD gene mutations may be useful for personalized management of patients with G6PD-deficient hemolytic anemia.