This study was designed according to the consensus statement of Meta-analysis of Observational Studies in Epidemiology (MOOSE) (12). Extended systematic search was carried out in databases of Medline (via Pub-Med), EMBASE (via OvidSP), ISI Web of Knowledge, Sco-pus, Cochrane Library, and ProQuest based on the key-words obtained from Medical Subject Heading (MeSH) terms and EMTREE. The keywords included “Ultraso-nography” OR “Sonography” OR “Ultrasound” OR “Chest Film” OR “Chest Radiograph” combined with “Pleural Ef-fusion” OR “Effusion” OR “Pleural Free Fluid”. The di-rective was to find prospective and retrospective studies assessing the diagnostic value of ultrasonography or chest radiography in detection of pleural effusion. Two of the authors (M.Y, P.G) independently searched for sources and contacted the authors of relevant articles to