Epidemiologic patterns of colorectal cancer (CRC) in Iran have not been studied adequately. In a recent cancer registry and active cancer surveillance, we collected data on the incidence of colorectal tumors in five provinces of Iran from 1996 to 2000. In total, 2055 were registered in this study. Age-adjusted rates of CRC in Iranian males and females were 8.2 and 7.0/100,000, respectively. Seventeen percent of the cases were younger than 40 years of age at the time of diagnosis. This proportion was similar to proportions seen in many other Middle-Eastern countries, but much higher than those seen in Western countries. A comparison of age-specific rates between Iran and the US showed similar rates in young (<40 years) Iranians and Americans, but much lower rates in older (>/=40) Iranians. We conclude that Iran is still a country with low-risk of CRC, particularly for older individuals. The high proportions of young CRC cases seen in Iran, and probably many neighboring countries, are due to the young age-structure of these countries and relatively low rates of CRC in older individuals.