This work presents the first reported crystal structure determination of xanthine, the Form I polymorph, which has been achieved using 3D-ED techniques. As might be expected, the structure shows structural similarities to that of guanine. Its highly planar nature also lends itself to potential low energy planar defects and further, the existence of other polymorphs, which is suggested by the XRPD data. In addition, the data were of sufficient quality to allow all hydrogens to be located and independently kinematically refined without the use of geometric restraints. This work builds upon the use of 3D-ED to determine the crystal structure of β-guanine and unlocks possibilities for the structural comparison between biogenic and synthetic xanthine crystals which may help understand mechanisms behind crystal morphogenesis and the morphological and functional diversity of biocrystals .