Fanconi anemia (FA) is the most common genetic form of aplastic anemia, a recessive disorder characterized by a progressive pancytopenia, diverse congenital abnormalities and a predisposition to malignancy. Diagnosis is made by study of DEB-induced chromosomal breakage, a test developed by Dr. Arleen Auerbach. The disease frequency varies among ethnic groups and is particularly high in the Ashkenazi Jewish population, who are estimated to have a carrier frequency of 1 in 89. Clinical variability may be explained in part by genetic heterogeneity. Mutations in at least thirteen different genes can result in FA. The Rockefeller University Hospital is home to the International Fanconi Anemia Registry (IFAR), established in 1982 in order to study a large number of patients exhibiting the full spectrum of diverse features of FA. Questions relating to diagnosis, natural history of the disease, prognosis, treatment and cancer incidence in FA are being addressed by the IFAR studies. Information regarding genotype-phenotype correlation is being obtained; we hope this will help to determine the physiologic roles of the cloned genes.