Oxidation of acetaminophen at boron-doped diamond (BDD) and at Ti/SnO2 anodes in a plug-flow divided electrochemical reactor led to electrochemical combustion, whereas at Ti/IrO2 benzoquinone was the exclusive product except at very long electrolysis times. The difference is explicable in terms of the different mechanisms of oxidation: direct oxidation at the anode for Ti/IrO2 vs. indirect oxidation involving electrogenerated hydroxyl radicals at BDD and Ti/SnO2. At BDD, at which the efficiency of degradation of acetaminophen was greatest, the rate of electrolysis at constant concentration was linearly dependent on the current, and at constant current linearly dependent on the concentration. Current efficiencies for mineralization up to 26% were achieved without optimization of the cell design.