Diclofenac has been irradiated under UV-C light at 254 nm. The effect of some operating variables has been investigated, The kinetics of the process has been analysed by means of the corresponding quantum yield. The presence of free radical promoters has also been considered. Diclofenac initial concentration plays an important role in its conversion profile. First order kinetics is ruled out under the applied experimental conditions. The process efficiency is significantly enhanced if oxygen is bubbled instead of air. Diclofenac quantum yield values in the range approximate to 0.1-0.3 mol Einstein(-1) were obtained depending on the operating conditions used (air or oxygen) and the kinetic methodology followed. The mineralization level achieved also increased from 30 to 80% when oxygen was sparged instead of air. The presence of free radicals promoters did not improve the diclofenac removal efficiency. (C) 2010 Elsevier B.V. All rights reserved.