At present, concentrations of pharmaceuticals in surface and ground waters are low; however, even low concentrations of certain substances may prove very harmful. One of such pharmaceutical drugs is diclofenac, a popular non-steroidal anti-inflammatory drug (NSAID). For this reason, it is important to determine its mobility in groundwater and to estimate parameters of migration. Authors conducted column tests for two porous media: an artificial one, consisting of glass granules, and a natural one, i.e., sandur sand obtained from a site north of the city of Poznań (Poland). During the test, impulse breakthrough curves of chloride ions and diclofenac were recorded. The results were used to identify a specific sorption model and to determine values of migration parameters. Solutions of the inverse problem using optimisation methods and of equations of mathematical migration models were carried out in a MATLAB environment. Based on test results, the mobility of diclofenac is shown to be very high and comparable to that of chloride ions. The tests also revealed a slight and irreversible sorption of diclofenac on grains of both porous media.