We report the synthesis of unusually thick poly(2-hydroxyethyl methacrylate) (PHEMA) films on gold surfaces by surface-initiated atom transfer radical polymerization (ATRP). Polymerization from the surface occurs rapidly at room temperature in aqueous media, resulting in the formation of 700 nm thick polymer films in just 12 h. Control experiments using neat monomer and catalyst (no water) yield films with thicknesses of only 6 rim, demonstrating the accelerating effect of water on surface-initiated ATRP. Kinetic studies reveal a nearly linear increase in thickness with reaction time, indicating that chain growth from the surface is a controlled process with some "living" character. A second block can be grown from dormant initiators at the end of PHEMA chains, providing further evidence of "living" chain ends. Derivatization of the hydroxyl groups of grafted PHEMA with a variety of molecules allows dense functionalization of these films. Reflectance FTIR spectroscopy shows a virtually quantitative yield in derivatization reactions, and the increase in film thickness after surface derivatization correlates with the molecular mass of the newly formed repeat unit.