Purpose: To evaluate the use of positron emission tomography using 18F-fluorodeoxyglucose (FDG-PET) to assess early response to pre-operative chemoradiation therapy in combination with external locoregional hyperthermia in patients with oesophageal cancer by correlating the reduction of metabolic activity with histopathologic response. Material and methods: Twenty-six patients with histopathologically proven intra-thoracic oesophageal cancer (with ≤2 cm gastric involvement), scheduled to undergo a 5-week course of pre-operative chemoradiation therapy and hyperthermia, were included. FDG-PET was performed before (n = 26) and 2 weeks after initiation of therapy (n = 17). FDG uptake was quantitatively assessed by standardized uptake values. Results: After neoadjuvant therapy, 24 of the 26 patients underwent surgery. In 16 patients changes in FDG uptake were correlated to histopathologic response. In these patients, histopathologic evaluation revealed less than 10% viable tumour cells in eight patients (responders) and more than 10% viable tumour cells in eight patients (non-responders). In responders, FDG uptake decreased by a median -44% (-75 to 2); in non-responders, it decreased by a median of -15% (-46 to 40). At a threshold of 31% decrease of FDG uptake compared with baseline, sensitivity to detect response was 75%, with a corresponding specificity of 75%. The positive and negative predictive values were both 75%. Conclusion: FDG-PET is a promising tool for early response monitoring in patients undergoing chemoradiation therapy in combination with hyperthermia.