Flaxseed has been used for centuries for oil extraction. In recent years it has attracted considerable interest as a result of studies which attribute potential health benefits to its components. Among the compounds that present biological activity, phenolic compounds are of special interest. The dietary lignan secoisolariciresinol diglucoside (SDG) reaches high concentrations in flaxseed. Flaxseed contains also other phenolic compounds, such as phenolic acids. Considering the importance of the phenolic fraction of flaxseed, high performance analytical methods have been developed to characterize its complex phenolic pattern. The understanding of the nature of these compounds is crucial for their possible exploitation in drugs and functional foods.