Although Marfan syndrome has been a recognized clinical entity for nearly a century, only in the early 1950s were its manifestations and genetic features firmly and fully established. Similarly, although the identification of the basic defect in Marfan syndrome had been vigorously pursued for several decades, it was only in 1991 that two independent reports implicated fibrillin as the defective gene product. Surprisingly and serendipitously, these studies also revealed genetic heterogeneity of the fibrillin proteins and established linkage between one of these loci and a Marfan-related disorder, congenital contractural arachnodactyly. Like Marfan syndrome, this condition is accompanied by skeletal abnormalities; however, flexion joint contractures replace the loose-jointedness of Marfan syndrome and, more importantly, neither the eye nor the aorta are affected. More recently, a similar association with the fibrillin gene has also been established in the dominantly inherited form of ectopia lentis. These associations of structurally related gene products with Marfan and related syndromes may conceivably imply that other connective tissue disorders are caused by mutations in these or other yet undiscovered fibrillin genes.