Patients with sickle cell disease (SCD) often require blood transfusion starting in early childhood. Multiple blood transfusions on a chronic basis lead to excessive accumulation of iron, especially in adults with sickle cell anemia (SS) that is progressively increasing in size. Blood exchange transfusion and the use of iron chelation therapy may prevent or delay the onset of iron overload. The majority of adults with SS, however, require episodic blood transfusions on a chronic basis and, hence, are at risk to develop iron overload. Recent reports suggest an association between iron overload and organ failure in chronically transfused patients. Patients with SCD and iron overload may thus be at increased risk to develop organ failure compared to those with normal iron stores. In order to clarify this issue we have prospectively collected the following data on our adult patients with SCD between 1978 and 1998: (1) the amount of blood transfused; and (2) the status of iron stores determined with serum ferritin, serum iron, total iron binding capacity (TIBC), and percent transferrin saturation (% Sat). Between 1987 and 1998, 247 adult patients with SS were regularly followed in our sickle cell center. Of these, 152 (62%) were transfused with 4,875 units of red blood cells (RBCs). Transfused patients received an average of 10 units of RBCs per year, which is equivalent to about 2.0 g of iron per year. This does not include transfusions at other institutions or before 1987. About one third of the adult patients with SS had % Sat greater than 50 in the steady state, suggesting iron overload. During painful episodes serum ferritin increased significantly in paired observations. Serum iron and TIBC decreased during painful episode disproportionately so that there was a significant net decrease in % Sat in paired observations. Patients with low values of serum ferritin and % Sat had lower incidence of acute painful episodes (38% v 64%) and organ failure (19% v 71%) than those who had iron overload, respectively. Mortality was significantly higher in the iron overload group: 64% versus 5%, respectively. Taken together, the data indicate that (1) the status of iron stores in adults with SS is best determined by keeping accurate records of the amount of blood transfused and serial determinations of ferritin levels in the steady state; (2) a significant number of adults with SS have iron overload; and (3) iron overload seems to be a predisposing factor of disease severity.