Historical changes in the human environment have highlighted that mortality rates due to causes affected by behavior to increased. Many of these causes disproportionately affect males. This study, based on evaluating the ratio of male to female mortality rates by age and main causes of death in 2006, offers a picture of the sex differences in mortality rates in Iran. The findings indicate that the ratio of male to female death rates, for total causes of death, particularly in young ages, are higher. According to the index, regarding each category of causes of death, i.e., exogenous causes, endogenous causes, and accidents, mortality rates for males are higher than females. Sex differences, related to the ratio of deaths from accidents is more pronounced. Among the events, deaths from traffic accidents have the most important contribution to the higher mortality in men compared with women, so that in age group 20-24, death rates are 7 times higher among males. Also, males lost 50% more years of life than females due to unintentional injuries. Results indicate the dominant role of behavioral factors, along with changing causes of death, in the excess mortality of males over the females.