Herpes simplex virus 1 (HSV 1) is a common infection that causes painful ulcers of the mouth and lips “cold sores”. JE is a 72-year-old male who developed HSV 1 of his neurotised intra-oral ulnar forearm free flap. Subjective flap swelling was initially reported by the patient, who subsequently went on to develop vesicles, with swabs revealing HSV1 infection. There were no other peri-operative complications. Complete recovery of the free flap was achieved with a course of valaciclovir. On literature review, there is only one previous report of HSV 1 infection on a free flap.