This study is an observational (ie, noninterventional), longitudinal, multicenter, global registry for patients with pyruvate kinase (PK) deficiency, a rare nonspherocytic hemolytic anemia. This Registry will be open for enrollment for 7 years and all enrolled participants will be followed prospectively for a minimum of 2 years, and up to 9 years. Data will be collected from participating Registry Physicians, participants, and, where appropriate, parents/guardians who have provided informed consent or assent (where relevant) and authorization pursuant to applicable laws and regulations. Data should include demographic, clinical, and treatment data; and other data of relevance to the management of patients with PK deficiency. Annual chart review and data entry are expected in order to enhance longitudinal understanding of PK deficiency; however, no specific protocol schedule of assessment is required by this Registry protocol.