The interferon regulatory factor 6 (IRF6) gene and environmental factors have been shown to be associated with nonsyndromic cleft lip with or without cleft palate (NSCL/P) in several populations. This study aimed to confirm the contribution of IRF6 and environmental factors to NSCL/P risk in western Han Chinese. Five single nucleotide polymorphisms (SNPs) were investigated in 107 case trios (child and parents) and 100 normal peers in western China using transmission disequilibrium test, case-control analysis, and logistic regression models. Strong evidence of linkage disequilibrium was found between these markers and the disease in both SNP analysis (A allele at rs4844880, G allele at rs2073485, and C allele at rs599021) and haplotype analysis (A-A for rs861019 and rs4844880, A-C for rs4844880 and rs599021, among others). Both mothers' medication and passive smoking during the first trimester of pregnancy may increase the risk of NSCL/P, but mothers' vitamins (including folic acid) supplementation during the first trimester was a protective factor. Interactions between mothers' abortion history and TT genotype of rs2235373 were statistically significant (odds ratio = 6.70, 95% confidence interval =1.69-26.52). Risk factors identified in this study may provide a better understanding of the etiological role IRF6 and environmental factors play in NSCL/P incidence.