The effect of social factors on the male/female difference in mortality in Finland was studied by comparing age-adjusted mortality of males and females by social class and marital status. 44,548 death certificates (years 1969-1971) and 1970 census data for 25-64-years olds were analysed. The gender difference was 2.8-fold: 5.3-fold for violent causes and 2.3-fold for natural causes. The greatest gender difference from violent causes was found in accidental poisonings (18.7-fold) and drownings (12.8-fold), and from natural causes in mental disorders (mainly alcoholism; 5.7-fold) and in ischemic heart disease (4.5-fold). The gender difference was most prominent in unskilled workers, divorced and widowed and less prominent in married and upper professionals. The great variation of gender difference of mortality by social class and marital status seems to indicate that mortality difference between males and females is associated to external factors rather than biological differences between men and women. This conclusion is also supported by the progressive increase of gender difference of mortality from 1.4 to 2.8 during the last 80 years in working-aged Finns.