A retrospective study was undertaken in 1990 of 188 patients with the diagnosis of non small cell carcinoma of the lung referred to the Department of Radiation Oncology in 1984. Most patients (178/188) received a course of radiotherapy. This was definitive in 23, palliative in 148 (primary site in 113, metastases in 16, primary plus metastases in 19) and postoperative in 7. This report is a 5 year followup of the 171 patients treated by radiation alone, to assess factors that influence survival. Tumour histology was 50% squamous, 23% adenocarcinoma, 16% large cell and 4% unspecified, non small cell carcinoma. In 8% no histological diagnosis was obtained. The most common symptoms were cough (44%), dyspnoea (43%), chest pain (37%), haemoptysis (33%) and systemic symptoms (36%). Tumour stage (TNM) was assessed retrospectively as I(5%), II(8%), IIIA(18%), IIIB(22%) and IV(28%). A subgroup of 31 cases (18%) of uncertain staging (I-III) was analysed separately and in 2 cases (1%) no staging information was available. Palliative intent of treatment and poorer performance status were related significantly to increasing stage of disease. The effects of palliative treatment were recorded in 79 cases; in 71 there was a reduction in symptoms. The median survival from diagnosis was 8 months (range < 1-72). Using univariate and multivariate analyses, significant and independent prognostic factors for improved survival were good performance status, absence of systemic symptoms, lower tumour stage and curative intent of treatment (higher radiation dose). However the 5-year survival was only 2%. Long-term survival was associated predominantly with early stage disease but not with the type or intent of treatment.(ABSTRACT TRUNCATED AT 250 WORDS)