Tuberculous peritonitis is an insidious disease without clearly indicative clinical, laboratory , or radiologic findings. Therefore, the diagnosis of this disease is diffi cult. We present a liver cirrhosis patient who had simultaneous tuberculous peritonitis and reactivation of cytomegalovirus (CMV) infection. The diagnosis of tuberculous peritonitis could have been missed due to concurrent cytomegalovirus viremia and lymphadenitis and because lymphadenopathy was initially believed to be caused by malignancy. Positron emission tomography and computed tomography (PET/CT) scans revealed an increased uptake of the dye over the lymph nodes of the right supraclavicular region, left subclavicular region, and the right-side of the pelvis. These fi ndings were initially considered to be indicative of malignancy related lymphadenopathy. The diagnosis of tuberculous peritonitis was confi rmed by paracentesis and Mycobacterium culture of the ascetic fl uid. Diagnostic paracentesis with Mycobacterium culture of the ascetic fl uid, and endoscopy with biopsy may provide conclusive evidence for the diagnosis of peritoneal tuberculosis.