We have recently analysed by histological, protein and molecular DNA techniques 23 mutations of the collagen III gene (COL3A1), most of which cause premature arterial fragility, thin skin and variants of vascular Ehlers-Danlos syndrome. There were 14 glycine substitutions between residues 637 and 1021, eight exon skips between exons 7 and 45 and one small inframe deletion. The glycine substitutions produce a gradient of increasingly abnormal clinical phenotypes from exons 36 to 49 while the clinical severity of exon skips is much more variable. Each mutation is private for the affected family or individual concerned having the potential for early prenatal diagnosis and prevention.