To monitor the influence of dementia on the health of the population the concept of Dementia-Free life Expectancy (DemFLE) was introduced. The DemFLE was estimated using Sullivan's method on the data of the ERDA study 1991 (Epidemiology Research on Dementia, Antwerp, Belgium). At the age of 65 years, elderly people in Belgium had a life expectancy of 16.4 years, a DemFLE of 15.3 years, and 1.1 years with at least moderate dementia. In absolute years the life expectancy with dementia remained constant beyond the age of 65: it was about 1.7 years for women, 0.7 years for men. The proportion of the remaining life that will be lived in a demented state increased with age: 4% and 9% in men and women at age 65, but 20% and 30% at the age of 85. The results confirm dementia as an important public health problem in the elderly.