Background Lung cancer survival after radiotherapy remains poor and greater knowledge of normal tissue risk factors is needed to further optimise treatments. In this work, we investigate tumour laterality in a large cohort of patients treated with curative-intent radiotherapy, including the effect of dose on the right and left lungs. Methods 1101 NSCLC patients were included in the analysis, treated with 55Gy in 20 fractions. Tumour laterality was determined by comparing the centre of mass of the tumour volume with the centre of mass of the lung. Right and left lungs were segmented from the whole lung contour and the mean dose to each volume calculated. Laterality and mean lung doses were included in multi-variable cox-regression survival models. Results1026 patients were eligible for inclusion; 579 right-sided and 447 left-sided tumours were identified. All tumour and patient characteristics were balanced with laterality. The multi-variable models were controlled for known clinical factors: tumour volume (p<0.001), age (p<0.001), performance status (p<0.05) and nodal stage (p<0.01). Multi-variable analysis showed laterality to be highly significant (p<0.01) with right-sided tumours showing worse overall survival than left-sided tumours (15 versus 18 months). The right lung mean dose was found to be significant (p=0.03) for overall survival but the left lung mean dose was not (p=0.78). Conclusion Our study showed that right-sided lung tumours show worse overall survival for NSCLC treated with curative-intent radiotherapy. Results suggest that the effect of laterality is through a difference in dose-response for individual lungs, with the larger, right lung, having the greater impact on survival.