Objective: gastric cancer is the fourth most common cancer worldwide. While it is one of the most common cancers in Iran, there are only limited data regarding incidence trends in the country. This study is the first of its type to investigate trends across six geographical areas during 2000-2005 using cancer registry data. Materials and methods: The registered data for gastric cancer cases in National Cancer Registry System were extracted from the Ministry of Health and Medical Education, Center for Disease Control & Management, code C16. First, according to WHO population, the sex-standardized incidence rate in both sexes and then the trends of incidence rate during 2000-2005 were investigated separately for different geographical areas of the country. Results: the incidence rates of gastric cancer in Iran and its six geographical areas during 2000-2005 were increasing albeit with differences in their slopes. The overall incidence rate increased from 2.8 in 2000 to 9.1 per 100,000 persons per year in 2005, rising from 4.1 to 13.2 in men. The average six-year incidence of gastric cancer in the central and northwestern border of Caspian Sea was 7.8 per 100,000 persons per year, while it was 0.9 per 100,000 persons per year in the border of the Persian Gulf. Generally the incidence rate in men was higher than in women. Conclusion: Iran is one of the high-risk areas for gastric cancer. Increase in incidence might continue in the future partly because of improvement in cancer registry systems as well as increase in risk of this cancer.