We report a case of tuberculous peritonitis in a 24-year-old male patient. On admission, he was complaining of abdominal fullness and fever. Ultrasound tomography and computed tomography (CT) scan of the abdomen showed massive ascites with multiple septa. The most interesting feature of this case was the diffuse and intense uptake of gallium-67 in the abdomen. Though the initial chest X-ray showed only slight bilateral pleural effusion, and cultures from ascites, stool, sputum, and pleural effusion were negative for Mycobacterium tuberculosis, CT scan of the lung showed a small consolidation shadow with contractile change, similar to tuberculosis. A few days after the CT scan of the lung, the sputum was positive for Mycobacterium tuberculosis. Finally we diagnosed active tuberculous peritonitis, and then started antituberculous therapy. In patients with massive ascites and fever of unknown origin, tuberculous peritonitis must be considered. Gallium-67 scintigraphy has been shown to be useful when there is a high index of suspicion of tuberculous peritonitis.