Introduction: Tuberculosis (TB) infection is still a challenging health issue, especially in developing countries. Diagnosing extrapulmonary infections, especially isolated organ involvement, is difficult in most cases even with the radiological, endoscopic, and histopathological examinations done for accurate diagnosis. Here we describe a case of isolated gastric TB with specific F-18 fluorodeoxyglucose (FDG) positron emission tomography (PET)/computed tomography (CT) findings mimicking gastric cancer/ lymphoma. Case report: A 20-year-old male patient was admitted to our hospital with abdominal pain in the epigastric region, weight loss, and fever especially at nights for 2 months. Physical examination was normal. Hemoglobin was 9.6 gm/dL; the patient had iron deficiency anemia. Upper gastrointestinal (GI) endoscopy was suggestive of gastric ulcer mimicking malignancy. F-18 FDG PET/CT revealed multiple hypermetabolic malignant lymphadenopathies in the abdomen and diffuse gastric wall thickening as linitis plastica and multiple hypermetabolic peritoneal implants in the omentum. Exploratory laparotomy was done for tissue diagnosis and exploration of the peritoneum for TB infection, lymphoma, and Crohn's disease to make differential diagnosis. Histopathology revealed granulomatous lymphadenitis with granulomas including giant cells, suspecting TB. Patient was put on antituberculosis treatment (ATT). After treatment, the complaints resolved, and he gained weight. Fusion PET/CT exhibited a complete response to ATT with no residual disease. Conclusion: According to our knowledge, this is the first report about F-18 FDG PET/CT findings in the diagnosis of isolated gastric TB. F-18 FDG PET/CT may provide help in the diagnosis and follow-up of isolated gastric TB in challenging cases.