>Several years ago, considerable controversy developed about this concern, but at present the issue seems to be settled. Should an individual with this problem not have a source of oxygen while diving (out of air, drowning, equipment failure, etc.), then the cells would sickle. However, the low-oxygen tensions necessary to produce this phenomenon would have caused brain damage long before the red cells were involved. The person with sickle cell trait then is not at any greater risk from hypoxia (oxygen deficiency in body tissues) than the ordinary diver and is qualified for diving (if trained and physically fit otherwise). There are other blood disorders, such as hemoglobin C disease, hemoglobin D disease, thalassemia and others. Some of these patients are usually in good health and others are not. The decision to dive in these conditions has to be individualized.