. "Precision cosmology from X-ray AGN clustering" . . . . . . . . . . . "Abstract. We place tight constraints on the main cosmological parameters of spatially flat cosmological models by using the recent angular clustering results of XMM-Newton soft (0.5-2 keV) X-ray sources, which have a redshift distribution with a median of z\u223C 1. Performing a standard likelihood procedure, assuming a constant in comoving coordinates active galactic nuclei (AGN) clustering evolution, the AGN bias evolution model of Basilakos, Plionis & Ragone-Figueroa and the Wilkinson Microwave Anisotropy Probe5 value of \u03C38, we find stringent simultaneous constraints in the (\u03A9m, w) plane, with \u03A9m= 0.26 \u00B1 0.05, w=\u22120.93+0.11\u22120.19." . . .