The aim of this paper is to review the experience of radical radiation therapy and the prognostic factors of patient outcome for clinically localised, medically inoperable non-small cell lung cancer (NSCLC) patients. Clinically staged node-negative NSCLC patients who were not a surgical candidates due to co-morbid diseases but who were eligible for curative treatment, were reviewed in the London Regional Cancer Program (LRCP). This study population was treated between 1st Jan 1985 to 31st Jan 2004. Patients were excluded if they were previously treated with chest radiotherapy. Patients with localised disease, but who refused surgery, were also included in the study. Eligible patients received radiation therapy which was given via localised portals and underwent simulation prior to therapy. The dose prescription range was from 50 Gy in 2.5 Gy per fraction to 60 Gy in 2 Gy per fraction. Hazard ratios and P-values were determined for time to recurrence and patient survival. A total of 74 patients met the study eligibility criteria. The median age of the cohort was 70 years (range 38-92 years). The cohort consisted of 52 males and 22 females. 39/74 (53%) had a pathological diagnosis of squamous cell carcinoma. Clinical stages were 21 (28%) T1 , 40 (54%) T2 , and 13 (18%) T3 , respectively. 59/74 (78%) completed their planned radical radiotherapy but 15/74 declined radiotherapy. The median follow-up time was 17.6 months (range 0.4-123.6 months). For patients who completed radiotherapy, the two-year and five-year disease-free survival (DFS) rates were 38.1% and 11.4%. Overall survival (OS) two-year and five-year rates were 33.2% and 6.9%, respectively. The median DFS and OS for T1 , T2 , and T3 were 18.7, 14, 15 months; and 23.1, 18.5, 14.5 months, respectively. Patients who received radiotherapy compared to those who did not, had median lung cancer-specific survival (CSS) times of 21 months and 4.9 months (P<0.001); OS times of 20 months and 5 months (P<0.001), respectively. Tumour size had impact on patient survival in univariate (P=0.004) and multivariate (P=0.002) analyses. In conclusion, radical radiotherapy significantly improves survival for patients with medically inoperable clinically staged localised NSCLC, and tumour size is a predictor of patient outcome. The OS, CSS, and DFS rates for patients with tumour size greater than 6 cm are significantly worse than those with smaller size tumours.