This study presents the first population-based report on breast cancer in the Islamic Republic of Iran using data derived from a cancer registry. A retrospective study was conducted to find all new breast cancer cases in 5 provinces covered by the cancer registry during the 5-year period 1996-2000. There were 2421 cases recorded in the 5 registries. The age-standardized incidence rate (ASR) was 16.2 per 100 000 person-years. In contrast to more developed countries, the ASR of breast cancer was low, with the lowest rate seen in Ardabil province.