The anti-inflammatory drug diclofenac is found worldwide in natural water bodies and toxicological investigations report harmful effects for aquatic species even at low concentrations. Diclofenac is one of the pharmaceutical substances on the first watch list of the European Water Framework Directive. If it will be categorized as a priority substance, emission limits will be established. One of the discussed methods of diclofenac reduction in wastewater are advanced oxidation processes. In this paper, the degradation of diclofenac in water was investigated using a sonoelectrochemical system, consisting of an ultrasound transducer with a frequency of 850 kHz and boron doped diamond electrodes. With the combination of acoustic cavitation and electrochemical oxidation, as advanced oxidation processes, more than 90% of diclofenac could be degraded within 5 min at an initial concentration of 50 mu g L-1. These studies provide optimization of ultrasound density, voltage and electrode positioning on diclofenac degradation. The reaction was found to follow pseudo first order kinetics with a rate constant of 0.505 min(-1). Samples were concentrated with solid phase extraction and analyzed by high pressure liquid chromatography using a diode array detector. The formation of oxidative species was visualized by chemiluminescence of luminol. (C) 2015 Elsevier B.V. All rights reserved.