The deposition of copper on boron-doped diamond thin-film electrodes was investigated, Three kinds of boron-doped diamond films were studied: a film deposited on a silicon wafer, a second grown on a tungsten substrate. and a third, similar to the first, but surface-amorphized (bombarded) by ion beam irradiation. The films were investigated by a number of techniques. Linear potential sweep experiments in 0.1 M H2SO4 + 0.001 M CuSO4 solution showed that, besides the peak due to bulk copper deposition, a "prewave" peak is present in the voltammogram of the first two electrodes and not in the third one. An electrochemical activation at negative potential was imperative for the appearance of the "prewave" peak. The amount of copper involved was less than 2% of a monolayer. The comparison between spectroscopic and electrochemical investigations leads to the interpretation that the "prewave" peak corresponds to an underpotential deposition of Cu on graphitic inclusions in the diamond electrode, or along the grain boundaries, probably by intercalation.