The interfacial behaviour of thiourea (TU) in perchloric acid solutions on glassy carbon electrodes during silver electrodeposition has been studied using surface enhanced Raman spectroscopy (SERS). The spectroscopic results are compared with those obtained on electrochemically activated silver electrodes. Potential-dependent thiourea adsorption (occurring via sulphur) and ClO4- coadsorption an observed. No evidence for the adsorption of solution silver-thiourea complexes regardless of TU concentration was found. The time evolution of the TU SERS signals during the electroreduction of silver is a function of the crystallite formation (nucleation) and stabilization.