Synchrotron powder X-ray diffraction, X-ray absorption spectroscopy (XAS), and proton nuclear magnetic resonance (1H-NMR) data have been used to examine the structure of hypoxanthine, 1,7-dihydro-6H-purin-6-one (C5H4N4O), a purine base that participates in numerous metabolic processes. XAS and 1H-NMR spectroscopy were used to determine that hypoxanthine was present in its keto form (both in solid state and dissolved in an organic solvent). Rigid body refinement was performed with the Rietveld software package GSAS yielding triclinic lattice parameters of a = 7.1179 (2) Å, b = 9.7830 (3) Å, c = 10.4009 (3) Å, α = 58.876 (1)°, β = 67.609 (1)°, and γ = 71.937 (2)° (C5H4N4O, Z = 4, space group P$\bar 1$).