Anti-tumor properties assigned to PEDF, beside its role as an inhibitor of angiogenesis, make it a promising candidate in the search of new biomarkers for malignancy. In this study levels of PEDF were investigated in pleural effusions from lung adenocarcinoma and benign inflammatory disease patients. The mean PEDF concentration in the malignant group was slightly superior to that in patients suffering benign diseases (4.59 μg/mL vs 3.97 μg/mL), although the difference did not reach statistical significance (P 0.166). Pleural effusion PEDF levels were not related to gender, age, smoking habit or pleural effusion size. We also investigated the possible relationship of PEDF levels in pleural effusion regarding clinicopathological features. Correlations were found for monocytes (P 0.010) and polymorphonuclear leukocytes (P 0.023) with PEDF levels in pleural effusion of malignant origin.