Conventional tests are not always helpful in making a diagnosis of tuberculous pleurisy. Many studies have investigated the usefulness of interferon (IFN)-γ measurements in pleural fluid for the early diagnosis of tuberculous pleurisy. We conducted a metaanalysis to determine the accuracy of IFN-γ measurements in the diagnosis of tuberculous pleurisy. Methods: After a systematic review of English-language studies, sensitivity, specificity, and other measures of accuracy of IFN-γ concentrations in the diagnosis of pleural effusion were pooled using random-effects models. Summary receiver operating characteristic curves were used to summarize overall test performance. Results: Twenty-two studies met our inclusion criteria. The summary estimates for IFN-γ in the diagnosis of tuberculous pleurisy in the studies included were as follows: sensitivity, 0.89 (95% confidence interval [CI], 0.87 to 0.91); specificity, 0.97 (95% CI, 0.96 to 0.98); positive likelihood ratio, 23.45 (95% CI, 17.31 to 31.78); negative likelihood ratio, 0.11 (95% CI, 0.07 to 0.16); and diagnostic odds ratio, 272.7 (95% CI, 147.5 to 504.2). Conclusions: IFN-γ determination is a sensitive and specific test for the diagnosis of tuberculous pleurisy. The measurement of IFN-γ levels in pleural effusions is thus likely to be a useful tool for diagnosing tuberculous pleurisy. The results of IFN-γ assays should be interpreted in parallel with clinical findings and the results of conventional tests. (CHEST 2007; 131:1133–1141)