Introduction: Intraperitoneal ascites is a consequence or combination of many different underlying diseases. Laparoscopy with peritoneal biopsy is a tool for rapid and accurate diagnosis. Methods: We retrospectively identified patients who could not be diagnosed by clinical examination, laboratory investigations, and imaging tests. Results: A total of 103 (55 male and 48 female) patients were selected. The median age of the study group was 54 years (range 38–64 years). Typical clinical symptoms included fever (58.2%), abdominal pain (56.3%), and digestive disorders (62.1%). Fever and digestive disorders were higher in the peritoneal tuberculosis (TB) group than in the metastatic cancer group [(62.1% vs. 12.5%, P=0.009) and (66.3% vs. 12.5%, P=0.004)]. Abdominal pain was more common in the metastatic cancer group than in the other groups (100% vs. 55.8%, P=0.020). Patients in the TB and chronic inflammation groups had lower red blood cell counts and blood albumin (41 vs. 42, P=0.039) than those in the metastatic cancer group, respectively. The rate of intestinal wall thickening on ultrasound and peritoneal thickening on computed tomography was higher in the cancer group than in the benign group (87.5% vs. 7.4%, P=0.000) (75% vs. 23.2%, P=0.005), respectively. There was no difference in the median peritoneal fluid volume between the two groups (390 vs. 340, P=0.058). Pathological results showed 88.3%, 7.8%, and 3.9% of peritoneal TB, metastatic cancer, and chronic inflammatory lesions, respectively. The median hospital stay did not differ between the two groups (4 vs. 3 days, P=0.051). Both groups of patients had no morbidity or mortality. Conclusion: Unidentified ascites and peritonitis must be difficult for making diagnose by conventional methods. Laparoscopy might be supportive of making a rapid diagnosis and starting early treatment.