The structural polymorphism of DNA/lipopolyamine (multi-cationic lipid) complexes has been studied by X-ray diffraction and cryo-electron microscopy. Monovalent salt and temperature effects have been analyzed. Depending on the treatment applied to the lipidic solution prior to DNA addition, two types of structure can be obtained for identical final conditions: a classical lamellar structure and a more complex structure, The latter was shown to appear when the lipidic solution prepared in high salt condition is vortexed and quenched below the hydrocarbon chain melting temperature, before addition to the DNA solution. It corresponds to some small facetted vesicles. Similar behavior is observed for the poly(styrene-sulfonate)/lipid system.