Records of patients with non-operative stage III non-small cell lung cancer registered at the Department of Radiotherapy, Cancer Institute Hospital, from January 1978 to June 1980 were examined in order to present prognostic information on survival. The data were derived from 100 carefully staged patients and include results from the patients' history, physical examination, pretreatment laboratory tests, radiological findings, nature of radiotherapy and response to treatment. Serum albumin, tumor site, performance status (PS), hemoglobin, TDF and response were identified as important prognostic factors in the univariate analyses. On the other hand, tumor site, PS and serum albumin were significantly related with survival in the multivariate analyses. However it was found that TDF and response significantly affected survival when posttreatment variables were taken into account. These patients were classified into low, intermediate and high risk groups according to those three pretreatment factors (tumor site, PS and serum albumin), and the median survival times for the groups were 10.3 months, 10.4 months and 2.5 months, respectively. These results suggest that high risk patients with stage III non-small cell cancer generally might be treated palliatively.