Counterfeit medicines are a growing problem in the world, for their use may endanger patient's health and therefore they pose an enormous public health risk. The manufacture of counterfeit medicines usually involves organised crime groups which place the counterfeit medicines on the market for reasons of profit. Detection and prevention of trade in counterfeit medicines requires close cooperation between medicine regulatory authorities, police, customs, judiciary and pharmaceutical industry. To this day, there have been no recorded cases of counterfeit medicines in the legal supply chain in Croatia. However, medicines without marketing authorisation in Croatia, originating from different countries, could be found on the illegal market. Most frequently, this includes medicines for the treatment of erectile dysfunction such as: sildenafil, tadalafil, vardenafil. In this study, 26 medicines for the treatment of erectile dysfunction, seized in illegal supply chain, were tested. High performance liquid chromatography (HPLC) was used for identification and quantification of active substances in the tested samples. It was determined that 13 out of 26 samples did not comply with declared composition of medicine and quality specification. Furthermore, two samples did not contain declared active substance vardenafil and that may indicate that these medicines are counterfeit.