['Nitric oxide (NO), mainly synthesized by inducible nitric oxide synthase (NOS2) in pathological conditions, plays an important role in cytotoxicity, inflammation and fibrosis. Elevations in exhaled NO after thoracic radiation have been reported to predict radiation-induced lung injury (RILI). This study examined whether genetic variations in NOS2 gene is associated with the risk of RILI.', 'A cohort of 301 patients between 2009 and 2011 were genotyped for 21 single nucleotide polymorphisms (SNPs) in the NOS2 gene by the Sequenom MassArray system. Kaplan-Meier cumulative probability was used to assess RILI risk and Cox proportional hazards analyses were performed to evaluate the effect of NOS2 genotypes on RILI.', 'Multivariate analysis found that three SNPs (rs2297518, rs1137933 and rs16949) in NOS2 were significantly associated with risk of RILI⩾2 (P value=0.001, 0.000092, 0.001, respectively) after adjusting for other covariates. Their associations were independent of radiation dose and mean lung dose. Further haplotype analysis indicated that the ATC haplotype of three SNPs is associated with reducing the risk of developing RILI.'] Are genetic variants in inducible nitric oxide synthase gene associated with the risk of radiation-induced lung injury in lung cancer patients receiving definitive thoracic radiation?