In this paper, we compare the structural information obtained by measuring X-ray diffraction reciprocal space maps and by EXAFS analysis on two Si(1-x)Ge-x, alloys with low (LC) and high (HC) Ge concentration. From the analysis of the X-ray diffraction maps we determined the alloy lattice parameters for the cubic cell (a = 5.58 Angstrom) of the fully relaxed HC sample and for the tetragonal cell (a = 5.43 Angstrom, c = 5.46 Angstrom) of the fully strained LC sample and from these values the Ge alloy content (HC: x = 0.66 +/- 0.04, LC: x = 0.048 +/-0.003). The EXAFS data were taken at the Ge k-edge for incident wave polarization directions either parallel or perpendicular to the surface plane. The satisfactory correlation found between the Ge coordination ratio and the Ge-Si and Ge-Ge distances, derived by best-fitting the EXAFS curves, and the X-ray diffraction structural parameters indicates that the combination of the two techniques is a unique approach to achieve a thorough characterization of the structural and chemical properties of lattice mismatched heterostructures.