The voltammetric behavior of hydrogen peroxide at a glassy carbon electrode in alkaline solution was studied. An anodic prewave, preceding the well-known transport controlled oxidation reaction of hydrogen peroxide, was observed. The voltammetric current in this wave is independent of the rotation speed of the glassy carbon disc electrode, even in what looks like a limiting current plateau, denoted by a pseudo limiting current. This current is dependent strongly on pH and temperature, does not vary linearly with hydrogen peroxide concentration and the reaction orders, with respect to hydrogen peroxide and hydroxyl ions (pH), are dependent on the hydrogen peroxide concentration. A mechanism that call explain these experimental results has been proposed. It consists of two submechanisms, occurring simultaneously at the electrode surface, which are in competition with each other. Their relative predominance is controlled by the hydrogen peroxide concentration, which can explain the varying reaction orders with respect to hydroxyl ions and hydrogen peroxide. The current equation resulting from the proposed mechanism shows the possibility of using the studied electrode reaction for the amperometric determination of hydrogen peroxide up to high concentrations.