From 1986 to 1988 84 patients with tuberculosis were treated in the Intensive Care Unit of the Thorax Clinic Heidelberg (2.8% of total admissions). Only 18% (n = 15) of the cases were referred in the course of conservative treatment while 82% (n = 69) were admitted after thoracic surgery. In 49 of these patients (71%) the diagnosis of tuberculosis could be confirmed only postoperatively by histological examination. This diagnosis should be considered in any ICU patient belonging to the typical groups at risk or showing clinical signs of tuberculosis, e.g. weight loss, chronic productive cough and fever. For the confirmation of the diagnosis both microscopic examination and mycobacterial cultures are necessary. In cases of open tuberculosis in which mycobacteria are identified in sputum, urine or fistula secretion, the most important step of infection prophylaxis is the isolation of these patients (single rooms) and the prevention of airborne transmission by using face masks and protective gowns.