The electrochemical oxidation of phenol in basic media using a diamond thin-film electrode has been studied. Within the parameter ranges used (temperature: 15-60 degreesC, initial total carbon concentration: 360-1450 mg of C dm(-3); current density: 15-60 mA cm(-2)), almost complete mineralization of the organic waste is obtained. The mineralization rate increases with current density and temperature. Current efficiency depends mainly on mass transfer limitations: in the absence of mass transfer limitations, instantaneous current efficiencies of 1 are obtained. The main intermediates formed are maleic, fumaric, and oxalic acids. A simple model based on mass transfer and kinetic considerations, which involves four species (phenol, maleic/fumaric acid, oxalic acid, and carbon dioxide), can be used to explain the experimental behavior of the system, regardless of the conditions applied.