We have studied the colour centre production by swift electronand heavy ion irradiations of yttria-stabilized zirconia (YSZ),i.e. ZrO2:Y with9.5 mol% Y2O3. For this purpose, we performed irradiations of - or -oriented YSZ single crystals with 2.5 MeV electrons, 145 MeV13C, 180 MeV32S, 200 MeV58Ni, 230 MeV79Br, 120 MeV127I, 200 MeV127I, 200 MeV197Au, and2.6 GeV 238U ions. X-band electron paramagnetic resonance (EPR) and UV–visible optical absorptionmeasurements were used to monitor the point defect formation. The EPR line saturationswere measured between 6 and 150 K, in order to obtain the spin–lattice relaxation time(T1).Electron and ion beams produce the same two colour centres: (i) the first one is identified as anF+-type centre (singly ionized oxygen vacancy) with an axial symmetry, a small g-factor anisotropy ( and ) and long T1 values, (ii) the second one is similar to the well known T-centre(Zr3+ in a trigonal oxygen environment) with an axial symmetry and a large g-factor anisotropy ( and ), which is also produced by photon irradiations. A broad optical absorption band centred at awavelength near 500 nm is observed with an absorption coefficient proportional to the volume densityof the F+-type centre deduced from the room temperature EPR spectra. Since nochange of this band occurs between 10 and 300 K, it indicates that theelectron–phonon coupling of this colour centre must be strong, in agreement with anF+-type centre. Owing to the axial symmetry and lack of hyperfine structure of the EPR lines of this defect, it is suggestedthat the first coordination shell must contain one native oxygen vacancy. The plotsof the volume density of this centre versus fluence are on the whole rescaled asfunctions of the number of displacements per atom induced by elastic collisions.