This paper aims to investigate the age pattern and level of mortality in Iran focusing on causes of death. For this purpose, we used data from the "Registration and Classification of Causes of Death System" in 2008. To analyze causes of death and its effects on mortality structure, two techniques of mathematical demography including multiple decrement life tables and decomposition were applied. Evaluation of mortality data showed that underreporting and the report of age at death for 80+ ages are two main problems. After correction of data, life expectancy at birth for women and men was found to be 72.7 and 70.7, respectively. The age pattern of mortality in Iran differs from other populations in two important aspects. First, the sex ratio of mortality for young ages (between ages 15-39) is higher than the expected level. This is because of the high level of deaths from injuries in Iran compared with other countries, as the multi-decrement life tables indicate. The second difference in the mortality age pattern in Iran, in comparison with other countries, is the under-expected sex ratio in 70+ ages. Cause decomposition of differences in life expectancy of women and men showed that non-communicable diseases in the last age groups have led to more deaths in women than in men.