This study was initiated to assess the validity of the traditional view that superior vena cava syndrome (SVCS) is a life-threatening condition requiring immediate treatment without necessarily obtaining a tissue diagnosis. A retrospective review of 6504 patients diagnosed to have lung cancer and treated at the Queensland Radium Institute between 1979 and 1991 was performed. From this group, 249 patients with well-documented SVCS treated with radiotherapy were identified. An analysis with respect to duration of symptoms, time to treatment, degree of response and overall survival was performed. Although deaths did occur in this series due to associated tracheal obstruction, deaths due to venous compression per se were not seen. The response to radiotherapy was generally poor, with only 19% of patients achieving a complete resolution of their symptoms and signs while 30% of patients had no demonstrable response. The overall survival of patients in the study group was 5% at two years. Patients demonstrating a complete or partial response to treatment survived significantly longer than patients who did not respond at all. The median survival for complete responders was 6 months while for non-responders it was 1 month. Although 71% of patients had commenced radiotherapy within 24 h of presentation, many patients had been experiencing symptoms or signs of SVCS for quite some time. Only 29% of patients had experienced symptoms for 7 days or less while 49% of the study group had experienced symptoms for over 2 weeks.(ABSTRACT TRUNCATED AT 250 WORDS)