Microsomal epoxide hydrolase (EPHX1) is an important gene because of its role in the metabolism of components of cigarette smoke; thus it may be an important potential modifier of the risk of developing smoking-related lung disease, such as chronic obstructive pulmonary disease (COPD). Several studies have investigated EPHX1 and COPD, but some of these studies have potentially been affected by genotyping error. We investigated the influence of single nucleotide polymorphisms (SNPs) in EPHX1 on well-characterized COPD and intermediate phenotypes. A total of 1,232 participants completed a detailed respiratory questionnaire and spirometry. From this sample, 72 COPD cases (FEV₁/FVC < 0.70 and FEV₁ < 80% predicted) and 220 control subjects (no respiratory symptoms and normal lung function) were selected for analysis. The EPHX1 exon 3 and EPHX1 exon 4 polymorphisms were carefully genotyped to avoid error using several methods. We found that the EPHX1 exon 3 polymorphism was not associated with an increased risk of COPD, nor was the EPHX1 exon 4 polymorphism. In addition, none of the EPHX1 haplotypes were associated with an increased risk of any COPD phenotype. This finding, along with doubt shed on the accuracy of other studies that have demonstrated positive associations, suggests that a strong role for the EPHX1 polymorphisms in respiratory disease is unlikely.