Peritoneal tuberculosis (TB) is a considerable problem in certain developing nations. Current diagnostic tests for peritoneal TB are difficult and time-consuming. This study aimed to determine the effectiveness of an adenosine deaminase (ADA) assay and the QuantiFERON-Gold (QFT-G) assay in the rapid diagnosis of TB peritonitis. Forty-one patients with a presumptive diagnosis of TB peritonitis with ascites were admitted to Mansoura University Hospital and included in the study. Ascitic fluid and blood samples were collected from each patient. Fluid samples were examined biochemically (protein concentration), cytologically (white blood cell count) and microbiologically (Ziehl-Neelsen stain and TB culture in Löwenstein-Jensen media), and ADA levels were determined using colorimetry. Interferon-γ levels in whole-blood samples were measured using the QFT-G assay. Fourteen (34 %) patients received a final clinical diagnosis of TB peritonitis; these patients were subclassified as definite (positive culture for Mycobacterium tuberculosis; eight patients), highly probable (four patients) and probable (two patients) for TB peritonitis. Of the 14 patients with a final clinical diagnosis of TB peritonitis, 3 (21 %) tested positive using an acid-fast bacilli smear, which showed a sensitivity of 21 % and a specificity of 100 %. A receiver operating characteristic curve showed that a cut-off value of 35 IU l(-1) for the ADA level produced the best results as a diagnostic test for TB peritonitis, yielding the following parameter values: sensitivity 100 %, specificity 92.6 %, positive predictive value (PPV) 87.5 % and negative predictive value (NPV) 100 %. The QFT-G assay yielded the following values: sensitivity 92.9 %, specificity 100 %, PPV 100 % and NPV 96.4 %. The ADA and QFT-G assays might be used to rapidly diagnose TB peritonitis and initiate prompt treatment while waiting for a final diagnosis using the standard culture approach.