Nodular histiocytic hyperplasia of the pleural is a benign proliferation of histiocytes admixed with various amounts of mesothelial cells. Nodular histiocytic hyperplasia has been reported in other tissues and areas of the body including endometrium, peritoneum, pericardium, and hernia sacs. Nodular histiocytic hyperplasia usually is an incidental finding, occuring equally in men and women, and is considered to be a benign reactive condition. The main differential is with a neoplastic process either primary or metastatic, and can be a pitfall in small lung biopsies or in lung transbronchial biopsies.