The invention relates to a cassette, in particular an X-ray cassette, for receiving a storage fluorescent screen. The cassette has on one of its narrow sides an opening through which the storage fluorescent screen is to be inserted into or removed from the cassette. The opening is closable by a flap which is displaceable between a closed position in which it closes the opening and a release position in which it releases the opening for insertion or removal of the storage fluorescent screen. For this purpose the flap is mounted swivellably to the transition between the narrow side of the cassette provided with the opening and the base of the cassette or the cassette lid.