The disclosure relates to crystalline valomaciclovir having characteristic absorption peaks at 22.9 deg. +/- 0.2 deg., 18.6 deg. +/- 0.2 deg., 19.5 deg. +/- 0.2 deg., 24.3 deg. +/- 0.2 deg., 20.8 deg. +/- 0.2 deg., 21.8 deg. +/- 0.2 deg., 27.0 deg. +/- 0.2 deg., 14.7 deg. +/- 0.2 deg., 15.5 deg. +/- 0.2 deg., 25.5 deg. +/- 0.2 deg., and 29.9 deg. +/- 0.2 deg. in an X-ray powder diffractogram. The disclosure also relates to pharmaceutically acceptable salt of valomaciclovir which possesses the desired pharmacological activity of the parent compound and is suitable for the treatment or prevention of a viral infection selected from varicella zoster virus, herpes simplex viruses (HSV-1 and HSV-2), human herpes viruses (HHV-6, HHV-7 and HHV-8), Epstein Barr virus, cytomegalovirus, and HIV infection. The disclosure further relates to a process of preparing crystalline valomaciclovir, comprising the steps of: (a) dissolving valomaciclovir in a lower alkanol solvent or a mixed solvent of lower alkanols by heating to an appropriate internal temperature (b) cooling the solution with stirring to effect substantial crystallization of valomaciclovir and(c) collecting the crystalline valomaciclovir.
