In the title compound (systematic name: 3,8-diamino-5-ethyl-6-phenylphenanthridin-5-ium 2,2,3,3,4,4,4-heptafluorobutyrate), C 21 H 20 N 3 + ·C 4 F 7 O 2 - , two ethidium ions, C 21 H 20 N 3 + form a dimerized structure due to π-π inter-actions, even though they are positively charged. The hepta-fluoro-butyrate anions are connected to neighbouring cation dimers via hydrogen-bonding inter-actions, the hydrogen-bonding donor sites of the -NH 2 groups of the ethidium ions connecting to the hydrogen-bonding acceptor sites of the -COO - groups of the hepta-fluoro-butyrate anions.