Abstract: The invention relates to a waterproof and form-fitting mobile telephone casing comprising a mainly rigid casing body (2) formed from a waterproof material and a substantially waterproof capping piece (3) and part of the shell of the casing body consists of transparent elastic material (4) so that the keys of a telephone placed inside the casing can be operated through the material (4). The casing body (2) comprises at least one waterproof and resilient bellows structure (6) for adapting the form of the casing body to the design and size of the mobile telephone to be fitted into the casing body.