OBJECTIVE: The purpose of the study was to carry out a candidate gene analysis in families with familial thoracic aortic aneurysms and dissections. METHODS: The study material consisted of 11 Finnish families (with 115 members genotyped) who underwent echocardiographic examination for measurement of the aortic root diameter. Selected candidate genes included the loci for Marfan and Ehlers-Danlos syndromes, the genes of matrix metalloproteinases 3 and 9 and tissue inhibitor of metalloproteinase 2 as well two loci on the chromosomes 5q13-14 and 11q23.2-q24, previously found to be linked to the disease. RESULTS: The chromosomal locus 5q13-14 was linked to the disease risk (nonparametric linkage score 3.0, P =.005) confirming the previous linkage. Other candidate genes and loci were excluded as major loci in these families. CONCLUSIONS: The identification of the gene at chromosomal location 5q13-14 causing the development of such diseases would give us important knowledge on the pathogenesis of the disease and enable the identification of subjects at risk. This in turn would lead to appropriate treatment before the occurrence of fatal complications and, likely, to the development of new treatment methods.