Acute splenic sequestration crisis (ASSC) is a life-threatening complication associated with sickle cell anemia (SCA) that consists of an acute fall in hemoglobin produced by red blood cell (RBC) sickling within the spleen. It is also one of the leading causes of death in children with SCA. Occlusion of the splenic vascular supply leads to parenchymal ischemia and tissue necrosis. ASSCs are considered an emergency because of their high morbidity and mortality. Untreated patients may die within 1-2 h due to circulatory failure. Management is supportive, sometimes with blood transfusion and total or partial splenectomy. The aim of this chapter is to bring the up-to-date knowledge of the epidemiology, pathophysiology, diagnosis, and treatment of ASCC. Other important items considered are the spleen dysfunction, susceptibility to infections, and its prevention, disease expression, and to address the different managements for improving prognosis.