Electrolysis cell in the constructive form of single elements, intended for instance for the production of chlorine, hydrogen and/or caustic soda and designed in such a way that the portion of inactive membrane surface is minimised thanks to an optimised flange type so that the ratio between the flange surface of a semi-shell and the active membrane surface can be set to less than 0.045, neither the semi-shells nor the membrane being provided with bores or recesses for accommodating the clamping members.