Intrathoracic fibromas are rare tumours, but as might be expected they have been described in many different situations within the chest in relation to areas of connective tissue. In a personal series of 198 primary intrathoracic neoplasms, excluding carcinoma of the lung and oesophagus, Harrington (1950) encountered 13 fibromas or lipofibromas, all of which arose in the posterior mediastinum, but most of those which have been fully described appear in single case reports. Study of the available literature suggests that these tumours may be classified in four groups depending upon their position. Some have been found in the larger bronchi and occasionally diagnosed after biopsy through a bronchoscope. Others have been identified in relation to the parietal pleura, although some of these are undoubtedly fibrous tumours of neural origin. The third gi oup occurs in the mediastinum and the fourth comprises those which appear to arise beneath the visceral pleura. The growth may assume giant size before the onset of symptoms referable to the chest, and may obtain additional blood supply through adhesion to neighbouring structures. It is then difficult-and sometimes impossible-to define its origin. Clagett and Hausmann (1944) claim the biggest fibroma yet removed from the chest, a mass weighing 5 kg., filling the lower part of the right pleural cavity and extending behind the heart to the left side. This was so densely adherent that it was not possible to decide whether it arose beneath the visceral or parietal pleura. This paper is intended to describe our findings in some examples which fall in the fourth group, i.e., those which we believe arise in close relation to the visceral pleura.