Oral infection with Herpes Simplex Virus (HSV) is a frequent and well documented complication in immunosuppressed individuals including patients on immunosuppressive medication. We report the development of severe oral infection with HSV type 1 in a 34 year old woman with type 1 diabetes mellitus and end stage renal disease (ESRD) following cadaveric renal transplantation at the Western General Hospital, Edinburgh. The role of acyclovir in therapy and chemoprophylaxis is discussed.