Objectives: Positron emission tomography with CT (PET/CT) scanning is increasingly being used in head and neck cancer to assess response after radical concomitant chemoradiotherapy. The purpose of this study was to assess the use of PET/CT following chemoradiotherapy at our institution. Methods: All patients receiving radical chemoradiotherapy for head and neck cancer over a 9-year period were retrospectively identified. Outcome data including local control and overall survival were collected for all patients. The negative predictive value of PET/CT for local recurrence was calculated. Of those with a reported positive PET/CT scan the maximum standardised uptake values were compared with the incidence of local recurrence. Results: 92 patients were identified having a post-treatment PET/CT from a total of 301 patients receiving radical concomitant chemoradiotherapy. Median time from completion of chemoradiotherapy to PET/CT scan was 3 (range 2-8) months. Median follow-up in surviving patients was 19 and 25 months in the PET/CT and non-PET/CT groups, respectively. The negative predictive value for local recurrence was 91.8%. The median maximum standardised uptake values were 10.2 (range 3.1-33) and 6.89 (range 3.1-30) in those with local recurrence and with no local recurrence, respectively. Conclusions: Post-chemoradiotherapy PET/CT may aid subsequent management decisions. Patients with a negative PET/CT scan after radical chemoradiotherapy have a 91.8% chance of remaining free of local recurrence 19 months post-treatment. A higher maximum standardised uptake value on the post-chemoradiotherapy PET/CT may predict subsequent local recurrence and warrants further investigation. Advances in knowledge: Post-chemoradiotherapy PET/CT imaging aids subsequent management decisions.