The electrolysis of rubrene in a thin-layer electrochemical cell leads to formation of electrohydrodynamic (EHD) convection patterns. The well-known electrochemiluminescence produced in this process renders the convective structures clearly visible. The electrochemical mechanism leading to the EHD convection is analyzed. In particular, the importance of ionic salt concentration is elucidated. Example structures are shown, and the basic mechanism of their formation by convective flows is proposed.