Fibrillin is an important structural protein of the extracellular matrix. It is a large cysteine-rich glycoprotein with extensive intrachain disulfide bonds, likely contributed by multiple EGF-like repeats. We have previously published 6.9 kb of FBN1 cDNA sequence. FBN1 cDNA clones that extend the sequence 3089 bp in the 5' direction are described in this report. The deduced primary structure suggests that fibrillin is composed of multiple domains. The most predominant feature is the presence of 43 calcium binding EGF-like repeats. We demonstrate here that fibrillin molecules bind calcium. In addition, three alternatively spliced exons at the 5' end are described. Analysis of 5.8 kb of surrounding genomic sequence revealed a 1.8-kb CpG island spanning the alternatively spliced exons and the next downstream exon. Since FBN1 is the gene responsible for Marfan syndrome, the information presented here will be useful in identifying new mutations and in understanding the function of fibrillin in the pathogenesis of the disease.