Being currently not married is more common today than 25 years ago. Over this period relative differences in mortality by marital status have increased in several countries, mainly as a result of a sharp decline in mortality among the married. Using Finnish census data linked with death certificates, we show that these increases are not explained by the non-married population becoming more marginalized in socio-economic status or household composition. However, the increases in marital-status differences in mortality from accidental, violent, and alcohol-related causes of death in the 30-64 age group indicate that changes in the health-related behaviour of the non-married population may play a role. The public-health burden associated with not being married has also grown. At the end of the 1990s about 15 per cent of all deaths above the age of 30 would not have occurred if the non-married population had had the same age-specific mortality rates as the married population.