Marfan syndrome is a multisystem disorder of connective tissue that is inherited in an autosomal dominant fashion, and results from mutation of the FBN1 gene on human chromosome 15. There are a number of conditions of the connective tissue with a similar phenotype that can be confused with Marfan syndrome. Modifications of the diagnostic criteria have recently been published, facilitating the differentiation of Marfan syndrome from these conditions. It is still difficult to use modern genetic testing for diagnosis because Marfan syndrome can be caused by many different mutations in FBN1, a large gene with 65 coding segments, while mutations in other genes can cause overlapping phenotypes. Several clinical trials of drug therapy, including the antihypertensive drug losartan, are in progress.