INTRODUCTION: For many years life expectancy in Denmark has improved less than in other comparable western countries, e.g. Sweden. An unhealthy life style, in particular the consumption of alcohol and tobacco, has often been mentioned as a possible explanation. MATERIALS AND METHODS: Life expectancy and mortality in Denmark and Sweden has been compared by means of nationwide cause of death registries. Alcohol- and tobacco-related deaths are defined from death certificate diagnoses. The comparisons between the two countries are made by age standardised mortality rates and life expectancies for the period 1997-2001. RESULTS: 50 years ago Denmark had one of the highest life expectancies in the world, but is now at the bottom of the list when compared to similar countries. Life expectancy in Sweden is now almost three years longer than in Denmark. Before the age of 75 there were a total of 3700 premature deaths among Danish men and 3400 among Danish women. Relative excess mortality was highest among Danish men aged 35-64 with a relative excess mortality at 40-50%. Among women excess mortality was 50-60% in the age group 35-74 years. Overall, alcohol and smoking account for almost the entire difference between Danish and Swedish men and for 75% of the difference between Danish and Swedish women. CONCLUSION: A very substantial part of the Danish excess mortality and low life expectancy compared to Sweden can be attributed to high mortality related to alcohol and tobacco consumption. A reduction of this difference in life expectancy does not seem realistic without a reduction in the consumption of tobacco and alcohol.