An X-ray sheet film cassette is assembled of a bottom wall, side walls and a cover hinged to an upper part of one side wall. The lower part of the one side wall adjoining the bottom wall is reduced in thickness to form an abutment for the sheet film. The inner surface of the cover is provided with a resilient pressing pad which during the closing of the cover urges the sheet film against the abutment and in the closed condition of the cassette presses the film against the bottom. In this manner, when taking X-ray pictures of a part of patient's body which forms an angle relative to another body part, the unexposed section of the first mentioned body part which is adjacent the other body part, is minimized and well defined in position relative to the other body part.