Abstract: The watch case comprising a middle (2) containing a lining (4) and a back (9) detachably mounted in a lower opening of the middle by means of a pressure device. A band (12) of synthetic material constituting a seal is formed on the periphery of the opening, that band being made in one piece with the lining and connected to it by portions of synthetic material crossing appropriate passages (15) of the middle. The side walls (16) of the opening are at least partially devoid of lining and they work together with opposite surfaces (17) of the back in order to assure pressure coupling of the latter and compression of the band (12).