The results of direct DNA diagnostics in nine patients with Marfan syndrome, aged from two to 52 years old, and four unhealthy relatives with the same disease from two unrelated families have been presented for the first time in Russia. Eight mutations in the gene FBN1 were revealed. One patient demonstrated a substitution with unknown clinical importance, which was previously described in the SN P database as rsl 12287730 with a frequency of incidence of 0.1%. Out of the eight mutations, two (25%) were previously described, and the other six mutations (75%) were revealed for the first time. These mutations revealed by us were of the following types: three mutations (37.5%) produced a shift in the open reading frame (two deletions and one insertion), three mutations (12.5%) involved a splicing site, and one (12.5%) nonsense mutation was also noted. Our data contradict previous reports that claimed that the majority of mutations in the FBN1 gene represented missense mutations. Such inconsistency could result from a small size of the examined sample or from substitutions that produced alteration in the splicing site (as we have demonstrated here). The distribution of the revealed mutations was uniform along the whole gene. The results of the conducted comparative analysis of genetic and phenotypic indices was in complete agreement with previously reported results. The developed direct method of DNA diagnostics was fully informative, as we managed in all nine examined patients to confirm their clinical diagnosis using a molecular and genetic approach.