Objectives: The aims of this study were to assess the predictive value of HPV-positivity in cervical lymph node metastases for the detection of a primary tumor (PT), to investigate the influence of HPV-positivity in cervical lymph node metastases on tumor control and survival and to analyse the impact of the 8 th edition of the UICC TNM classification on staging and survival.Methods: Neck dissection specimen of 47 consecutively included patients were analysed by PCR-based HPV DNA-testing and p16-immunostaining and survival analysis by Kaplan-Meier and Cox proportional hazard regression models were performed. Results:After standard work-up algorithm in patients with suspected CUP 27/47 patients (57%) remained a CUP whereas in 20/47 (43%) a PT was detected (tonsils, lung, parotid gland, skin). 14/20 (70%) with detected PT and 9/27 (30%) with CUP had HPV-positive cervical lymph node metastases (LNM). Sensitivity, specificity, positive predictive value and negative predictive value of HPV-positivity in LNM for diagnosis of a PT in the oropharynx achieved 65%, 95%, 94% and 69%, respectively. In the subgroup of patients with CUP the 5-year overall/disease specific survival (OS/DSS) of patients with HPV-positive compared to HPVnegative LNM was higher (5y-OS 73% vs. 41%, p=0.01, 5y-DSS 73% vs. 53%, p=0.02). The use of the new UICC TNM classification leads to down staging of 65% of patients with detected PT and 33% with CUP. Furthermore, advanced N-category becomes an important negative prognosticator for OS (N≥2: HR 3.05, 95% CI 1.21-7.67, p=0.01). Conclusion:HPV-positivity in LNM directs the detection of PT in the oropharynx in patients with CUP. One third of LNM in patients with CUP were HPVpositive associated with improved OS and DSS. When applying the 8 th edition advanced N-category and UICC stages are negative prognosticators for survival supporting the role for integration of biomarkes in staging systems.