Aberrant signalling through the hepatocyte growth factor/scatter factor receptor Met has been implicated in various aspects of the development of human cancer including the promotion of tumour invasion, angiogenesis and metastasis. Moreover, experimental data indicate that activation of the Met receptor may be involved in cellular resistance towards antineoplastic treatments such as chemotherapy and ionizing radiation. We determined the prevalence and clinical impact of the Met-activating mutation Y1253D in patients with squamous cell cancer of the oropharynx treated by radical radiotherapy. To screen archival tissue for the presence of a low-abundance point mutation, we developed a sensitive screening method using real-time polymerase chain reaction along with peptide nucleic acid-based DNA clamping and melting curve analysis. By this approach, Met Y1253D was detected in tumours of 15 out of 138 patients (10.9%). Both univariate and multivariate survival analysis revealed Met Y1253D to be significantly associated with impaired local tumour control. Our results provide evidence that the Met-activating mutation Y1253D is present in a notable subset of patients with oropharyngeal cancer and indicate that it may interfere with radioresponsiveness of these tumours, supporting the notion of aberrant Met signalling as a potential target for radiosensitization.