A method of preparing a ready-to-use catheter by providing a catheter assembly that has a first compartment that includes a catheter therein. The catheter includes on at least a part of its surface an exterior coating designed to reduce the coefficient of friction after treatment with a liquid swelling medium, and a second compartment containing a liquid swelling medium. The method includes sterilising the catheter assembly, adding the liquid swelling medium to the first compartment for wetting/activating the exterior coating of the catheter, and storing the ready-to-use catheter. By using the method according to the invention, the sterilisation of the catheter is effectuated in a dry-state, ensuring that the known problems with wet-sterilisation are completely eliminated and the need for preparing complicated and expensive liquid swelling mediums are no longer required.