n-3 Long-chain polyunsaturated fatty acids (n-3 LC-PUFAs) reduce inflammation through several mechanisms; therefore, components of the metabolic syndrome (MetS) may be treated with n-3 LC-PUFAs not only because of their anti-inflammatory effect but also through other mechanisms that reduce vascular reactivity, oxidative stress, and insulin resistance. In this chapter, the positive effects of n-3 LC-PUFAs on each component of the MetS are analyzed. Although information regarding the effect of n-3 LC-PUFAs on obesity is discordant, it seems to either inhibit weight gain or decrease inflammatory status; thus, a positive effect is expected. Regarding the effect on hypertension, evidence shows that treatment with n-3 LC-PUFAs reduces blood pressure by modulating vascular reactivity and reducing arterial thickness. In the case of dyslipidemia, the triacylglycerollowering properties of n-3 LC-PUFAs are among the best established in vivo actions. These fatty acids also decrease the assembly and secretion of very-low-density lipoproteins (VLDL), increase the conversion of VLDL to LDL particles, and increase β-oxidation of other fatty acids in mitochondria. Finally, insulin sensitivity is improved by treatment with n-3 LC-PUFAs due to actions on lipid dysregulation, adiponectin production and by their role as ligands to peroxisome proliferator-activated receptors. In conclusion, evidence mainly from randomized trials supports the positive effect of n-3 LC-PUFAs in all four components of the MetS. Such beneficial roles act at the cellular and the molecular levels and have been demonstrated in animal and human experimental studies and at the community level. Therefore, use of n-3 LC-PUFAs may be widely recommended to decrease the MetS and subsequently decrease the risk for type 2 diabetes and cardiovascular disease.