© 2015, The Japanese Society of Nuclear Medicine.Background: PET–CT is important for evaluating the cancer stage preoperatively. In patients with locally advanced disease, who are candidates for curative treatment modalities following computed tomography (CT) and ultrasonography evaluation, PET–CT can show distant metastases and spare patients unnecessary surgical interventions. We aimed to evaluate the contribution of PET–CT scans compared to conventional imaging studies on the change of treatment plan in patients with locally advanced esophagogastric cancer from neoadjuvant to palliative setting. Materials and methods: In this study, 91 patients with histopathologically proven diagnosis of esophageal or gastric cancer in our clinic between the years 2010–2014 were included. Prior to PET–CT evaluation, all of the patients were evaluated with thorax and abdomen computed tomography. Seventy-six of these patients were further evaluated by PET–CT due to ambiguous findings on computed tomography and 15 of them for staging purposes. The patients, who were shown to have distant metastases on conventional radiological imaging, were excluded from the study population. Results: Ninety-one patients were included in the study. Their median age was 57 (range 30–80) years and three-quarters of the patients were male. Most of the patients were evaluated by PET–CT due to suspicion of distant metastasis (83.5 %). Primary sites of the tumors on PET–CT were: esophagus 38.5 % and stomach 61.5 %. Between CT and PET–CT tumor stage and pathological lymphadenopathy concordance rates were 75.8, and 69.2 %, respectively. On PET–CT evaluation 47.3 % of patients had distant metastasis. New metastases were detected in 34.1 % of patients by PET–CT despite entering to scanning field of tomography. Following the PET–CT evaluation due to detected metastasis, 47.3 % of patients’ treatment plan was changed from neoadjuvant to palliative therapy. Conclusion: In the current study, 47.3 % (n = 43) of patients had distant metastasis that were not detected by CT evaluation. These patients were spared unnecessary surgical interventions. Evaluating the locally advanced gastric and esophageal cancer patients for PET–CT new metastasis could be indicated when the treatment plan of these patients would be changed from curative to palliative.