Perioperative or preoperative radiochemotherapy (RCTx) is nowadays standard for locally advanced esophageal cancer in Europe, as randomized studies have shown a significant survival benefit for patients with multimodal treatment. As responders and nonresponders have a significantly different prognosis, a response-based tailored preoperative treatment would be of utmost interest. An established method is a metabolic response evaluation by 18F-fluorodeoxyglucose positron emission tomography (FDG-PET). The level of metabolic response is known to be dependent on the localization, tumor entity and type of preoperative treatment. Association of FDG-PET with later response and prognosis was shown for absolute standardized uptake values (SUV) or a decrease of SUV levels before and after therapy but there are also contradictory findings in the literature and no prospective validation. However, neither time points nor cut-off for metabolic response evaluation have been defined so far. The most interesting approach seems to be early response monitoring during preoperative chemotherapy, which has shown promising results in prospective single center trials (MUNICON I/II) during chemotherapy of adenocarcinoma of the esophagogastric junction (AEG), but needs to be validated in prospective multicenter trails.