The distinction between tuberculous peritonitis and peritoneal carcinomatosis is extremely difficult in patients with omental cake appearance on computed tomography and elevated CA-125 level. A 21-year-old female presented with abdominal distention, diarrhea, nausea, fever, weight loss, and night sweats. Serum CA-125 level was 563 U/L (normal range: <35 U/L) and other tumor markers were within normal range. Radiologic studies showed massive ascites, smooth minimal thickening and increased contrast enhancement of peritoneum, omental nodularities, hepatomegaly, and right pleural effusion. No underlying malignancy that could cause this condition was detected clinically and radiologically. Ultrasound-guided omental tru-cut biopsy was performed to exclude carcinomatosis peritonei. Histopathologic examination showed small-medium-sized granulomas with caseous necrosis. Molecular microbiology tests of biopsy specimens confirmed diagnosis of tuberculosis. In conclusion, tuberculous peritonitis should be in differential diagnosis of a patient with ascites, omental nodularities and elevated serum CA-125 levels.