The invention provides an assembly for preparing a medical device, in particular a urinary catheter, by releasing a fluid medium onto the device. The device is packed in a package which contains the fluid medium confined in a compartment. To ensure preparation of the device, the package is adapted to open the compartment and the package in one and the same opening action, preferably so that the compartment opens at the latest when the package opens. In that way, removal of the device from the package requires opening of the compartment and the device is therefore wetted automatically as part of the opening procedure.