In this study 297 institutionalized patients with primary degenerative dementia were investigated. Age at onset of dementia was determined and individual longevity quotients (i.e. actual duration of survival divided by expected survival) were calculated. Expected survival was derived from the Dutch life tables for the general population. Age at onset of dementia was 75.6 +/- 7.8 years (mean +/- SD). Duration of dementia until death was 7.2 +/- 4.1 years. Dementia of early onset (before age 76) was associated with a significantly reduced life expectancy (LQ = 0.70 +/- 0.30), but this was not found for onset after age 75 (LQ = 0.91 +/- 0.58). Duration of symptoms at the time of admission into a nursing home was not associated with severity of behavioural and cognitive impairments as measured with behaviour rating scales. However, the severity of behavioural impairments predicted 1-year survival after admission, as could be shown by multivariate analysis which corrected for the effects of age and sex.