Sickle cell anemia is an inherited blood disease that affects the red blood cells. People with sickle cell disease have red blood cells (erythrocytes) that contain mostly hemoglobin S, an atypical molecule that causes the cells to have a sickle, or crescent, shape. These irregularly shaped cells have difficulty flowing through blood vessels, causing pain. They also break down much more quickly than normal red blood cells, leading to anemia. This slide shows blood cells of someone with the sickle cell anemia trait. Normal and sickle-shaped red blood cells can be seen in the blood smear. Stained with Wright's stain.