A 39-year-old otherwise healthy HIV-negative man visited the outpatient clinic for sexually transmitted infections (STI) of the local health authority (GGD Amsterdam), because of a three-week history of a painless skin disorder on the tongue. He had no other symptoms and no history of skin rash or ulcerations. In the past few months, he had unprotected insertive and receptive anal and oral sexual intercourse several times. On physical examination of the upper side of the tongue, we observed multiple sharply demarcated annular and serpiginous greyish white plaques with a symmetric distribution, covering an oval erosion on the distal right side of the tongue (figure 1). Photographs were taken with the patient’s permission. No other abnormalities were observed on the skin or the oral and anogenital area. There was no cervical lymphadenopathy. His last venereal disease research laboratory (VDRL) test, six months ago, was negative.