An accumulation of peritoneal fluid can result from a variety of conditions, cirrhosis of the liver being responsible for about 75% of all patients with ascites. Malignancy accounts for 10-12% and cardiac failure for about 5%. The remaining 8-10% of ascites cases have a variety of causes, including tuberculosis, pancreatic disease and kidney disease. An early and accurate diagnosis often depends on an appropriate ascitic fluid analysis. Patients with known liver cirrhosis and clinical deterioration also need to have a paracentesis, with a determination of the ascitic fluid leukocyte and neutrophil count and adequate bacteriological cultures of their ascitic fluid. The diagnostic value of different ascitic fluid parameters and their ability to distinguish between several aetiologies and their complications, is discussed.