Oleothorax is a method of therapy for pulmonary tuberculosis that was largely abandoned in the 1950s. Its purpose was to cause collapse of the adjacent lung by mechanical means. In the absence of either reactivation of tuberculosis or the development of an empyema, an oleothorax may expand to such an extent as to cause respiratory distress and require removal. The mechanism for this expansion is the stimulation of pleural fluid production by the oil. It is also thought that it may act in a manner similar to a chronic subdural hematoma. This expansion may occur after the oleothorax has been stable for many years, and frequently it is asymptomatic. Four patients were reviewed: one in whom the expansion was so great as to cause respiratory distress, one in whom the enlargement was less rapid and asymptomatic, and two with longstanding oleothoraces in whom the enlargement was more subtle.