Introduction and Aims: The northeastern region of Iran has some of the highest rates of esophageal squamous cell carcinoma (ESCC) in the world.Materials and Methods: To investigate the role of polycyclic aromatic hydrocarbons (PAHs) in the etiology of ESCC in northeastern Iran, we measured urine 1-hydroxypyrene glucuronide (1-OHPG), a stable PAH metabolite, in 99 inhabitants of this area.Results: The median urine 1-OHPG in participants of this study was 4.2 pmol/ml. Forty-two subjects (42%) had levels ranging from 1 to 5 pmol/ml, indicative of moderate PAH exposure, and 41 (41%) had levels above 5 pmol/ml, indicative of very high exposure. Further analysis showed that 1-OHPG levels were high in all subgroups of our study subjects, including both sexes; rural and urban dwellers; and smokers and non-smokers. Only 15% of the variance in 1-OHPG was explained by age, sex, residence, smoking, nass, or opium consumption. This pattern of PAH exposure parallels with the ESCC incidence pattern seen in this area.Conclusions: We conclude that people in northeastern Iran are exposed to widespread and very high levels of PAH, largely from unknown sources, and this may contribute to the high rates of ESCC observed in this area.