A 58-year-old woman was admitted due to a pseudomembranous pharyngitis. The patient had not been vaccinated against diphtheria. Corynebacterium ulcerans was cultured from a throat swab. The production of diphtheria toxin by these bacteria was demonstrated with PCR and an immunoprecipitation test. The patient was cared for in respiratory isolation and was treated with benzylpenicillin. She quickly recovered and was discharged four days after admission. A contact investigation did not reveal any dissemination of the toxin-producing C. ulcerans and a source was not found. In spite of the large-scale vaccination against diphtheria which has taken place in the Netherlands since 1953, a physician has to consider diphtheria in the differential diagnosis of patients who present with a clinical syndrome compatible with this disease. Either Corynebacterium diphtheriae or C. ulcerans could be the pathogen responsible.