The Edinburgh Lung Cancer Group prospectively registered 651 new patients presenting with lung cancer during 1981; only 47 survived five years (7%). The survival rate was highest in patients selected for surgery (35/116, 30%) and in this group was related to cell type, stage of disease, and possibly to Karnofsky performance score (not statistically significant). By comparison with non-surgical patients these 116 patients undergoing surgery were highly selected in terms of age, favourable histological type, stage of disease, and performance score. Forty-two of the 535 non-surgical patients were given radical radiotherapy alone and seven (17%) survived five years. The remaining 493 received palliative radiotherapy, chemotherapy (alone or combined with radiotherapy), or symptomatic treatment alone; only five (1%) survived five years. Median survival was related to cell type (adenocarcinoma 2.6 months, squamous cell carcinoma 6.2 months), stage (stage I 8.5 months, stage III 4 months), and Karnofsky performance index (greater than or equal to 90 9.3 months, less than or equal to 50 1.2 months). Age and sex had no independent prognostic value in any group. Performance score was highly correlated with stage (and age) and in this study represented the "best prognostic factor" in clinical practice.