What is the benefit of being a carrier for sickle cell disease?

If you are a "carrier" of sickle cell disease you have one gene for sickle hemoglobin and one gene for normal hemoglobin (this is called Sickle Cell Trait). When a person with sickle cell trait or disease is infected with the malaria parasite, it enters the red blood cells, when then collapse ("Sickle"), which kills the parasite. It seems that this condition is "selected" in areas where malaria is endemic. The population without the sickle gene have a much higher risk of dying from malaria, while the group that has the sickle gene often have no symptoms.