e15598 Background: 1) To evaluate the usefulness of Positron Emission Tomography with combined 18F-Fluorodeoxyglucose with Computed Tomography (PET/CT) in the diagnosis of distant metastases in patients with gastric adenocarcinoma (GAC) compared to spiral double contrast thoracoabdominal Computed Tomography (CT); 2) To establish the utility of PET/CT in the detection of peritoneal carcinomatosis compared to laparoscopy. Methods: Thirty prospective patients (22 men, 8 women; mean age 67±11) who underwent endoscopic ultrasound and were classified as T2–3N1 or T3Nx GAC were included in this study. Whole body images were obtained 1 hour after injection of 370 MBq of 18F-Fluorodeoxyglucose. CT was performed within 2 weeks of PET/CT. Laparoscopy was performed without remarkable incidences. All findings were confirmed by histopathology examination and/or by at least 6 months follow- up. Results: Distant metastases were found in 9/30 cases: carcinomatosis (3), retroperitoneal (3) or mediastinal (2) pathological lymph nodes and one case of bone metastases (1). PET/CT diagnosed unsuspected distant metastases by CT in 4/9 patients (retroperitoneal (1) or mediastinal (2) pathological lymph nodes and 1 case of bone metastasis in the spine). In 1/3 patients with histopathological confirmed diagnosis of peritoneal carcinomatosis by laparoscopic findings was negative by PET/CT, and considered as a false negative case. On the other hand, 3 patients with initially positive peritoneal carcinomatosis by invasive laparoscopy were finally diagnosed as benign lesions. These lesions did not show significant uptake in PET/CT and were considered as true negative cases. Conclusions: 1) PET/CT is useful in the diagnosis of distant metastases in patients with GAC 2) Further studies are needed to establish the role of PET/CT to detect peritoneal carcinomatosis. No significant financial relationships to disclose.