Ataxia-telangiectasia or A-T is a fatal progressive neurological disease of children. The symptoms indicate disruptions in the development of such diverse body parts as cerebellum, thymus and chromosomes. The patients are unduly sensitive to ionizing radiation, immunodeficient, and a third of them develops cancer. All of this stems from defects of a single gene. Provided here is an up-to-date review of all important work in thefield. A wide spectrum of topics is covered, namely genetics, chromosome 11 mapping, radiobiology, complementation, heterozygote identification, clinical variants, biochemistry, and treatment of A-T.