Objective-Transthyretin can cause amyloidosis attributable to destabilization of transthyretin tetramers in plasma. We tested the hypothesis that genetic stabilization of transthyretin associates with reduced risk of vascular disease and increased life expectancy. Approach and Results-We included 68 602 participants from 2 prospective studies of the general population. We genotyped for 2 stabilizing genetic variants in the transthyretin gene (TTR), R104H and T119M, and determined the association of genotypes with plasma levels of transthyretin, measures of thyroid function, risk of vascular disease, and life expectancy. During a mean follow-up of 32 years, 10 636 participants developed vascular disease. We identified 321 heterozygotes for T119M (frequency, 0.47%); R104H was not detected. First, mean plasma transthyretin and thyroxine levels were increased by 17% (26 µg/mL) and 20% (19 nmol/L), respectively, in heterozygotes versus noncarriers (P=0.007 and P<0.0001), demonstrating functionality of this variant in the general population. Second, corresponding hazard ratios were 0.70 (95% confidence interval, 0.51-0.97) for all vascular diseases, 0.85 (0.59-1.23) for cardiovascular disease, 0.45 (0.25-0.81) for cerebrovascular disease, 0.47 (0.25-0.88) for ischemic cerebrovascular disease, and 0.31 (0.04-2.22) for hemorrhagic stroke. The cumulative incidence of cerebrovascular disease as a function of age was decreased in heterozygotes versus noncarriers (P=0.005). Third, median age at death from all causes, from vascular and cerebrovascular diseases, and after diagnosis of vascular disease, and median age at diagnosis of vascular disease, was increased by 5 to 10 years in heterozygotes versus noncarriers (P=0.002-0.05). Conclusions-These results are compatible with an association between genetic stabilization of transthyretin and decreased risk of cerebrovascular disease, and with increased life expectancy in the general population.