It has been suggested that iodine plays an important role in gastric cancer. Gastric cancer ranks first among the cancers in the north-eastern Anatolia region, Turkey, where iodine deficiency is common. In this study, iodine levels were determined in gastric cancer and surrounding normal tissues in 19 patients with gastric cancer. Tissue iodine levels were determined by the Foss method based on the Sandell-Kolt-hoff reaction. Tissue iodine levels were lower in gastric cancer tissue (17.8+/-3.4 ng I/mg protein, mean+/-SEM) compared with surrounding normal tissue (41.7+/-8.0 ng I/mg protein) (p<0.001). There was positive correlation between the iodine levels in gastric cancer tissue and surrounding normal tissue (r = 0.845, p<0.001). There was no significant difference in iodine levels in cancer and surrounding normal tissue between male and female subjects. The iodine deficiency in our region may be one of the factors for increased gastric cancer prevalence. Our results support the hypothesis that iodine plays an important role in gastric cancer development.