Over the 20th century sex differences in life expectancy in the industrialized countries have widened in favour of women. Recently, a reversal in the long-term pattern of this differential has been noted in some countries. In Canada, between 1981 and 2000, this differential narrowed by almost two years. Greater than expected improvements in male death rates with respect to heart disease, lung cancer, accidents and violence (excluding suicide) explain a large part of this phenomenon. Change in male and female smoking prevalence correlates strongly with change in sex differences in mortality from heart disease and cancer. The reasons underlying men's greater mortality improvements in regard to accidents and violence are less clear and need further investigation.