Ataxia-telangiectasia or A-T is a fatal progressiveneurological disease of children. The symptoms indicatedisruptions in the development of such diverse body parts ascerebellum, thymus and chromosomes. The patients are undulysensitive to ionizing radiation, immunodeficient, and athird of them develops cancer. All of this stems fromdefects of a single gene.Provided here is an up-to-date review of all important workin thefield. A wide spectrum of topics is covered, namelygenetics, chromosome 11 mapping, radiobiology,complementation, heterozygote identification, clinicalvariants, biochemistry, and treatment of A-T.