Some rare benign tumours may occur in the lungs and pleura; they are typically composed of plasma cells, lymphocytes, histiocytes, macrophages and various amounts of fibrous tissue. These tumours are called histiocytomas (Dubilier 1968, Ivanik & Mlekodaj 1968, Kinare et al. 1965, Titus et al. 1962, Wentworth et al. 1968), plasma cell tumours or plasmacytomas (Childress et al. 1950, Hellwig 1934, Legrand & Serfati 1968, Pätiälä & Perret 1962), plasma cell granulomas (Lane et al. 1955), xanthomas (Scott et al. 1948), xanthomatotic pseudotumors (Wentworth et al. 1968). Names such as “postinflammatory tumours” (Umiker & Iverson 1954), “sclerosing haemangioma” (Liebow & Hubbe 1956, Rubin et al. 1958, Turunen et al. 1957) and “vascular endothelioma” (Edwards & Taylor 1937) have also been used. Because of this variety of nomenclature it is difficult to find out how many of the growths published under different names actually are granuloma-like histiocytomas of the lung. However, the number of reported cases may be about thirty. Similar pseudotumours in the pleura have also been reported (Brown & Johnson 1951, Maisuk 1956). In the present work, the authors present three cases of histiocytoma-like tumours, two of which occurred in the lungs and one in the pleura. The authors draw attention to the morphological similarity between the pleural tumours and the lung tumours.