A major concern surrounding the redevelopment of brownfield sites is the potential presence of contaminants. In certain cases, these contaminants present a threat to the durability of structures in contact with the soil. Phenolic compounds are one such group of contaminants. This paper examines the influence of phenolic compounds on Portland cement hydration, as well as their diffusion into fresh cement pastes, as would occur in concrete placed in situ against contaminated soil. The influence of phenolic compounds on cement hydration varies widely depending on structure, and exposure to combinations of phenolic compounds produces effects that do not follow easily predictable patterns. While the apparent diffusion coefficients of phenolic molecules into hydrating cement pastes largely follow trends displayed by the compounds in water, there is some evidence of interaction of the molecules with cement paste. There is also evidence of the precipitation of binding of the compounds within cement paste. The practical implications of these findings are discussed.