1. A 38 year old male of Sicilian ancestry with a chronic, hemolytic anemia clinically indistinguishable from sickle cell disease is described. Family studies extending over three generations and including all persons indicate that this individual has received from his father a gene for the sickling phenomenon, and from his mother a gene for thalassemia.
2. Three alternative hypotheses are advanced to account for the severity of the anemia present in the patient. The bases whereby a decision can be reached as to which of the three hypotheses is correct are discussed. It is indicated that no decision is possible until the results of studying a number of families comparable to the present are available.
3. It is suggested that many of the reported cases of sickle cell disease in Caucasians actually involve a genetic situation comparable to the one reported in the present paper.