The clustering of X-ray selected active galactic nuclei (AGNs) appears to be a valuable tool for extracting cosmological information. Using the recent high-precision angular clustering results of ~30,000 XMM-Newton soft (0.5-2 keV) X-ray sources, which have a median redshift of z ~ 1, and assuming a flat geometry, a constant in comoving coordinates AGN clustering evolution, and the AGN bias evolution model of Basilakos et al., we manage to break the σ8 m degeneracy. The resulting cosmological constraints are Ω m = 0.27+0.03 –0.05, w = –0.90+0.10 –0.16, and σ8 = 0.74+0.14 –0.12, while the dark matter host halo mass, in which the X-ray selected AGNs are presumed to reside, is M = 2.50+0.50 –1.50 × 1013 h –1 M . For the constant Λ model (w = –1) we find Ω m = 0.24 ± 0.06 and σ8 = 0.83+0.11 –0.16, in good agreement with recent studies based on cluster abundances, weak lensing, and the cosmic microwave background, but in disagreement with the recent bulk flow analysis.