A hematologic disorder in which 50-90% of the red blood cells consist of rod forms and elliptocytes; often associated with a hemolytic anemia. There are several autosomal dominant forms [MIM*130500, MIM*130600, and MIM*179650], with one form linked to the Rh blood group, caused by mutation in the gene encoding erythrocyte membrane protein band 4.1 (EPB41) on chromosome 1p, whereas the unlinked form is due to mutation either in the alpha-spectrin gene on 1q, or in the beta-spectrin gene on 14q or the band 3 gene on 17q. There is one autosomal recessive form [MIM*225450] known. SYN: ovalocytosis.