A 46-year-old man appeared with white lesions of the oral cavity. A previously taken biopsy revealed no classifying diagnosis and treatment with mouth rinse produced no improvement. A new biopsy was taken, on which the pathologist performed additional tests. This resulted in the diagnosis ‘syphilis’. The patient was treated with benzylpenicillin and the oral white lesions disappeared. Although nowadays syphilis is rare, special attention is required when noticing these kinds of lesions of the oral cavity.