Central nervous system arteriovenous malformations are uncommon in hereditary hemorrhagic telangiectasia. Identical twins are described with hereditary hemorrhagic telangiectasia and concordance for central nervous system arteriovenous malformations identified by angiography. One twin had a central nervous system hemorrhage in the seventh month of pregnancy and also had a pulmonary arteriovenous malformation. The other was asymptomatic. A previously reported association between HLA type A2 BW17 and hereditary hemorrhagic telangiectasia was not confirmed. Two recombinations were identified between the loci for HLA and hereditary hemorrhagic telangiectasia. The loci for HLA and hereditary hemorrhagic telangiectasia are not closely linked. Stroke in a young person should prompt an inspection for manifestations of hereditary hemorrhagic telangiectasia.