In this work, the removal of dimethyl phthalate (DMP) by electrolyses and sonoelectrolyses with conductive-diamond anodes has been studied and compared. Both treatments have been shown to be very effective, attaining complete mineralization in the 1.6-160.0 mg dm(-3) range of initial concentrations of DMP. The current density strongly influences the rate and efficiencies of the processes, because of an increase in the pseudo-steady-state concentration of oxidants and the importance of processes occurring near the electrode surface. Ultrasound irradiation produces small differences in the depletion of DMP but significantly improves the chemical oxygen demand depletion rate, mineralization rate, and efficiency. Monomethyl phthalate, phthalic acid, and 4-hydroxyphthalic acid are the main aromatic intermediates, and maleic acid, tartaric acid, and especially oxalic acid are the most significant nonaromatic intermediates found. Concentrations obtained are very small in most conditions studied. In the presence of chloride ions, chlorophenols are found.