Objective: To evaluate the association between polycyclic aromatic hydrocarbon (PAH) exposure in oesophageal epithelial tissue and oesophageal squamous cell carcinoma (ESCC) case status in an ESCC case - control study in a high-risk population in north-eastern Iran. Methods: Tissue microarrays (TMAs) of non-tumoral oesophageal biopsies from patients with biopsy-proven ESCC and gastrointestinal clinic patients with no endoscopic or biopsy evidence of ESCC (control subjects) in a rural region in north-eastern Iran were immunohistochemically stained. Immunohistochemistry was performed using monoclonal antibodies 8E11 and 5D11 raised against benzoapyrene (BaP) diol epoxide (BPDE)-I-modified guanosine and BPDE-I-modified DNA, respectively. Staining intensity was quantified by image analysis and the average staining in three replicates was calculated. The main outcome measure was adjusted ORs with 95% CIs for the association between antibody staining intensity and ESCC case status. Results: Cultured ESCC cells exposed to BaP in vitro showed dose-dependent staining with 8E11 but not with 5D11. With 8E11, sufficient epithelial tissue was available in the TMA cores to analyse 91 cases and 103 controls. Compared with the lowest quintile of 8E11 staining in the controls, adjusted ORs for the 2nd to 5th quintiles were 2.42, 5.77, 11.3 and 26.6 (95% CI 5.21 to 135), respectively (p for trend