In 2011, the first commercial PET/MR scanner was introduced into the market. Head and neck cancer is supposed to be one field where this new technology might offer benefits over PET/CT, particularly with regard to local tumor staging. Several studies showed that PET/MR might be equal to PET/CT for the characterization of tumors and lymph nodes, or suggested various imaging protocols suitable for head and neck cancer staging. However, data about the actual clinical aim of PET/MR in head and neck cancer, i.e. the TNM staging using a whole-body imaging approach, are currently lacking. The purpose of this prospective study was to compare the diagnostic accuracy of contrast-enhanced PET/MR with that of contrast-enhanced PET/CT in determining the TNM stage of newly diagnosed head and neck cancer.Sequential contrast-enhanced PET/CT-MR was performed in 27 patients (median age 66, 16 males) with newly diagnosed head and neck cancer. MR sequences were: LAVA-Flex (whole body); axial T2-weighted, axial T1-weighted with and without contrast, sagittal and coronal T1-weighted with contrast, and DWI (head and neck). Four dually board-certified radiologists and nuclear medicine physicians with 7 – 10 years of experience in both MR and PET/CT analyzed the anonymized images in random order and blinded to all clinical data except for the suspicion of head and neck cancer. These 4 readers were separated into 2 review boards. Review board A first interpreted PET images alone, and then PET/CT images. A consensus decision was reached if the results of the two readers were different. Review board B interpreted PET images and PET/MR images in the same manner. TNM stage was assigned based upon the image analysis. If discrimination between two stages was not possible, readers were allowed to assign both stages. According to the standard of reference, the staging classification was rated as correct (score of 2) in case of accurate staging, correct but equivocal (score of 1) in case two stages were assigned with one of them being correct, or incorrect (score of 0) in case the assigned stage or stages were incorrect. The standard of reference consisted of histology, if available, and clinical and imaging follow-up (median 832 days, range 258 to 1176 days). In 13 of 27 patients (48%), the T stage was confirmed by surgery. In 14 of 27 patients (52%) the N stage was confirmed by surgery (neck dissection). Wilcoxon signed-ranks test was used. Twenty-seven patients with newly diagnosed and histopathology proven head and neck cancers successfully underwent PET/CT-MR imaging. Owing to contraindications, five subjects were not injected with contrast for the CT scan, and one of those also not for the MR scan. The T/N/M staging by PET/CT was correct in 17 patients (63.0%) / 19 (70.4%) / 22 (81.5%), equivocalin 8 patient (29.6%) / 3 (11.1%) / 3 (11.1%), and incorrect in 2 patients (7.4%) / 5 (18.5%) / 2 (7.4%).The T/N/M staging by PET/MR was correct in 20 patients (74.1%) / 21 (77.8%) / 26 (96.3%), equivocalin 6 patients (22.2%) / 2 (7.4%) / 1 (3.7%), and incorrect in 1 patient (3.7%) / 4 (14.8%) / 0 (0%).Consistently, the TNM staging by PET/MR was comparable to PET/CT (T: p = 0.331, N: p = 0.453, M: p= 0.034).Whole-body staging with PET/MR yields equal diagnostic accuracy as PET/CT in determining the stage of head and neck cancer.