Acanthocytosis represents an unusually pathological variant of red cell morphology which is encountered in a diverse group of inherited and acquired disease states. While the morphological features are similar in all instances, the biochemical lesions frequently differ. Most demonstrable abnormalities involve lipids although those acanthocytes associated with the McLeod phenotype are probably due to an alteration in a membrane protein. Acanthocytes, regardless of their etiology, usually have a decreased survival in the circulation owing to splenic sequestration and destruction.