Vaso-occlusion is the major cause of morbidity and mortality in sickle cell disease. The pathogenesis of vaso-occlusion likely involves many complex steps related to both the primary event of deoxyhemoglobin S polymerization and the many resultant pathologic changes in both the sickle erythrocyte and the vascular endothelium. Several therapeutic approaches have been designed to reduce the extent of deoxyhemoglobin S polymerization. Although direct chemical inhibition of deoxyhemoglobin S polymerization has proven difficult, strategies to increase levels of fetal hemoglobin or reverse sickle erythrocyte dehydration have been more successful. Although gene therapy is actively being pursued, the ability to cure sickle cell disease is currently limited to bone marrow transplantation with its attendant toxicities and limitations. Because the pathophysiology of vaso-occlusion in sickle cell disease is complex, its treatment will likely be optimized using a multifactorial therapeutic approach.