Computed tomography of the thorax and abdomen, from the thoracic inlet to the renal hila, was performed as part of initial staging in 51 patients with small cell carcinoma of the lung (SCCL). The computed tomographic (CT) scans were repeated after completion of chemotherapy, as part of routine restaging and assessment of response to therapy. To identify the ways in which CT scanning uniquely benefited evaluation of initial disease extent in comparison to other diagnostic studies exclusive of CT scan, all diagnostic and clinical data were reviewed. CT scan identified more advanced intrathoracic disease than chest radiography in 82% of patients. Mediastinal node involvement not appreciated by chest radiography was seen in 61% of patients. Adrenal and retroperitoneal node involvement, not suspected by other studies, was identified by CT scan in 31% and 12% of patients, respectively. Thirty percent of the patients staged as limited disease (LD) were advanced to extensive disease (ED) by CT scan findings. While confirmation, by biopsy, of positive CT findings was not consistently accomplished, restaging CT scans provided indirect confirmation by displaying improvement or worsening that correlated with disease regression or progression. Thoraco-abdominal CT scanning more accurately identifies the extent of small cell carcinoma than other imaging procedures. This has important implications for reporting results by extent of disease. In addition, CT more accurately identifies the magnitude of intrathoracic primary and nodal tumors, which may influence the choice and conduct of local treatment--surgery and/or radiation therapy--in combination with systemic chemotherapy.