In this work, we focus on the study of the structural and elastic properties of mercury digallium selenide (HgGa2Se4) which belongs to the family of AB 2 X 4 ordered-vacancy compounds with tetragonal defect chalcopyrite structure. We have carried out high-pressure x-ray diffraction measurements up to 13.2¿GPa. Our measurements have been complemented and compared with total-energy ab initio calculations. The equation of state and the axial compressibilities for the low-pressure phase of HgGa2Se4 have been experimentally and theoretically determined and compared to other related ordered-vacancy compounds. The theoretical cation-anion and vacancy-anion distances in HgGa2Se4 have been determined. The internal distance compressibility in HgGa2Se4 has been compared with those that occur in binary HgSe and ¿¿GaSe compounds. It has been found that the Hg-Se and Ga-Se bonds behave in a similar way in the three compounds. It has also been found that bulk compressibility of the compounds decreases following the sequence ¿¿-GaSe¿>¿HgGa2Se4¿>¿HgSe.¿ Finally, we have studied the pressure dependence of the theoretical elastic constants and elastic moduli of HgGa2Se4. Our calculations report that the low-pressure phase of HgGa2Se4 becomes mechanically unstable above 13.3 GPa. © 2013 American Institute of Physics ; Gomis Hilario, O.; Vilaplana Cerda, RI.; Manjón Herrera, FJ.; Santamaría-Pérez, D.; Errandonea, D.; Pérez-González, E.; López-Solano, J. (2013). High-pressure study of the structural and elastic properties of defect-chalcopyrite HgGa2Se4. Journal of Applied Physics. 113(1):735101-7351010. doi:10.1063/1.4792495 http://jap.aip.org/resource/1/japiau/v113/i7/p073510_s1. ; Senia ; 735101 ; 7351010 ; 113 ; 1