A method of making a ready-to-use catheter assembly is provided, which can be immediately used by a patient. The ready-to-use catheter assembly ensures that the catheter does not suffer from a loss of quality during its shelf life and a wetting medium are provided. The method comprises: placing a catheter with an inactivated hydrophilic outer surface at least along its insertable length and a wetting medium in a catheter package; treating the catheter package with the catheter and the wetting medium with electro-magnetic and/or particle radiation while at least initially the hydrophilic outer surface at least along the insertable length of the catheter remains inactivated; and activating the hydrophilic outer surface at least along the insertable length of the catheter with the wetting medium during and/or after the radiation treatment and wherein the wetting medium decreases in viscosity when submitted to electro-magnetic and/or particle radiation.