A configurable, dismantlable display case system, with supports for promotional graphics, for use as a display cabinet, the constitution thereof being simple and entailing a reduced cost, and with the possibility of changing the configuration of its assembly and the promotional campaign thereon. The modular display system consists generally of a plastic shelving unit, with trays at different levels, linked at their corners by means of pillars consisting of PVC profiles, of a generally triangular shape, which fit adjustably into corresponding housings, one at each corner and on both sides of each tray; short profiles formed by extruded PVC profiles of a more reduced length than the pillar profiles, of a generally triangular shape with rounded corners which slot adjustably into the corresponding housings of the tray, and comprising non-slip ferrules inserted into the profile forming the leg at the area in contact with the floor; and assembly method.